path: root/src/main.rs

use std::collections::HashMap;
use std::fs;
use std::io::{self, Write};

//use anyhow::Result;
use rand::prelude::*;
use rayon::prelude::*;
use serde::{Deserialize, Serialize};
use structopt::StructOpt;

mod charset;
mod datafiles;
mod example;
mod format;
use charset::Charset;
use datafiles::*;
use format::*;

#[derive(Debug, StructOpt)]
#[structopt(name = "datagengo", about = "Japanese example practice maker")]
struct Opt {
    #[structopt(subcommand)]
    cmd: Cmd,
}

#[derive(Debug, StructOpt)]
enum Cmd {
    ParseKanjidic,
    ParseJlptVocab,
    New {
        #[structopt(default_value = "10")]
        count: usize,
        #[structopt(long = "truncate")]
        truncate: Option<usize>,
    },
    Simplify,
    Cleanup,
    AddVocab,
    AddExamples,
    AddFurigana,
    Format,
}

fn main() {
    let opt = Opt::from_args();

    match opt.cmd {
        Cmd::ParseKanjidic => {
            let levels = parse_kanjidic().expect("error");
            for (level, chars) in levels.iter() {
                println!("{}: {}", level, chars.to_string());
            }
        }
        Cmd::ParseJlptVocab => {
            let kanji_levels = read_kanji_levels().expect("read_kanji_levels");
            let all_kanji =
                Charset::from_iter(kanji_levels.iter().map(|(_, c)| c.chars()).flatten());
            parse_jlpt_vocab(&all_kanji).expect("error");
        }
        Cmd::New { truncate, count } => {
            let kanji_levels = read_kanji_levels().expect("read_kanji_levels");
            let all_kanji = Charset::new(
                kanji_levels
                    .iter()
                    .map(|(_, x)| x.to_string())
                    .collect::<Vec<_>>()
                    .join(""),
            );
            let kanji_levels = kanji_levels
                .into_iter()
                .map(|(l, x)| (l, Charset::new(x)))
                .collect::<Vec<_>>();
            let mut ex = read_examples(&all_kanji).expect("read_examples");
            ex.retain(|e| (5..=25).contains(&e.ja.chars().count()));

            let mut batches = read_batches().unwrap_or_default();

            if let Some(t) = truncate {
                batches.truncate(t);
            }
            println!("---- starting after {} batches ----", batches.len());
            let target_len = batches.len() + count;
            gen_batches(&mut batches, target_len, &kanji_levels, &ex);

            save_batches(batches).expect("save_batches");
        }
        Cmd::Simplify => {
            let mut batches = read_batches().expect("read_batches");

            for batch in batches.iter_mut() {
                simplify_batch(batch);
            }

            save_batches(batches).expect("save_batches");
        }
        Cmd::Cleanup => {
            let mut batches = read_batches().expect("read_batches");

            let kanji_levels = read_kanji_levels().expect("read_kanji_levels");
            let kanji_levels = kanji_levels
                .into_iter()
                .map(|(l, x)| (l, Charset::new(x)))
                .collect::<Vec<_>>();
            cleanup_batches(&mut batches, &kanji_levels);

            save_batches(batches).expect("save_batches");
        }
        Cmd::AddVocab => {
            let mut batches = read_batches().expect("read_batches");

            let jlpt_vocab = load_jlpt_vocab().expect("load_jlpt_vocab");
            add_vocab(&mut batches, &jlpt_vocab);

            save_batches(batches).expect("save_batches");
        }
        Cmd::AddExamples => {
            let kanji_levels = read_kanji_levels().expect("read_kanji_levels");
            let all_kanji = Charset::new(
                kanji_levels
                    .iter()
                    .map(|(_, x)| x.to_string())
                    .collect::<Vec<_>>()
                    .join(""),
            );

            let mut ex = read_examples(&all_kanji).expect("read_examples");
            ex.retain(|e| (5..=25).contains(&e.ja.chars().count()));

            let mut batches = read_batches().expect("read_batches");

            add_extra_examples(&mut batches, &ex);

            save_batches(batches).expect("save_batches");
        }
        Cmd::AddFurigana => {
            let mut batches = read_batches().expect("read_batches");

            let jmdict = fs::read_to_string("data/JMdict_e.xml").expect("read_jmdict");
            let jmdict = roxmltree::Document::parse_with_options(
                &jmdict,
                roxmltree::ParsingOptions {
                    allow_dtd: true,
                    ..Default::default()
                },
            )
            .expect("parse_jmdict");
            let jmdict_idx = index_jmdict(&jmdict);

            let overrides = read_furigana_overrides().expect("read_furigana_overrides");

            for batch in batches.iter_mut() {
                for ex in batch
                    .examples
                    .iter_mut()
                    .chain(batch.extra_examples.iter_mut())
                {
                    ex.gen_furigana(&jmdict_idx, &overrides);
                }
            }


            save_batches(batches).expect("save_batches");
        }
        Cmd::Format => {
            let jmdict = fs::read_to_string("data/JMdict_e.xml").expect("read_jmdict");
            let jmdict = roxmltree::Document::parse_with_options(
                &jmdict,
                roxmltree::ParsingOptions {
                    allow_dtd: true,
                    ..Default::default()
                },
            )
            .expect("parse_jmdict");
            let jmdict_idx = index_jmdict(&jmdict);

            let batches = read_batches().expect("read/parse");

            fs::create_dir_all("public").expect("mkdir public");
            fs::copy("static/style.css", "public/style.css").expect("copy style.css");

            batches
                .iter()
                .enumerate()
                //.skip(25)
                //.take(1)
                .for_each(|x| format_batch(&jmdict_idx, batches.len(), x));

            let kanji_levels = read_kanji_levels().expect("read_kanji_levels");
            format_index(&batches, &kanji_levels).expect("format_index");
            format_about().expect("format_about");
        }
    }
}

// ----

fn read_batches() -> anyhow::Result<Vec<Batch>> {
    let json = fs::read("data/batches.json")?;
    Ok(serde_json::from_slice::<Vec<Batch>>(&json)?)
}

fn save_batches(batches: Vec<Batch>) -> anyhow::Result<()> {
    fs::write(
        "data/batches.json",
        serde_json::to_string_pretty(&batches)?.as_bytes(),
    )?;
    Ok(())
}

// =====================================================================
//                      BATCH STRUCTURES AND GENERATION
// =====================================================================

const CHARS_PER_BATCH: usize = 20;
const MAX_NEW_CHARS_PER_EX: usize = 5;

#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
struct Batch {
    level: String,
    chars: Charset,
    chars_p1: Charset,
    chars_p2: Charset,
    chars_bad: Charset,
    examples: Vec<Example>,
    #[serde(default)]
    extra_vocab: Vec<JlptVocab>,
    #[serde(default)]
    extra_examples: Vec<Example>,
}

fn gen_batches(
    batches: &mut Vec<Batch>,
    target_len: usize,
    kanji_levels: &[(String, Charset)],
    examples: &[Example],
) {
    let mut remainder = None;
    while batches.len() < target_len {
        let done = Charset::from_iter(
            batches
                .iter()
                .map(|x| x.chars.chars().iter().copied())
                .flatten(),
        );
        let remainder_chars = remainder
            .as_ref()
            .map(|x: &Batch| x.chars.clone())
            .unwrap_or_default();

        let remainder_before = remainder.clone();
        let len_before = batches.len();

        let mut advanced = false;
        for (i, (level, level_chars)) in kanji_levels.iter().enumerate() {
            let diff = level_chars.diff(&done).diff(&remainder_chars);
            if !diff.is_empty() {
                let avoid = Charset::from_iter(
                    kanji_levels
                        .iter()
                        .skip(i + 1)
                        .filter(|(l, _)| !l.ends_with("-9") && !l.ends_with("-10"))
                        .map(|(_, c)| c.chars().iter().copied())
                        .flatten(),
                );

                let level_examples = level_examples(&diff, &avoid, examples);
                let level_new_chars = Charset::from_iter(
                    level_examples
                        .iter()
                        .map(|x| x.chars.chars().iter().copied())
                        .flatten(),
                )
                .inter(&diff);
                println!(
                    "- {} ({} chars): {} done previously, {} diff, {} ex, {} new chars",
                    level,
                    level_chars.len(),
                    done.len(),
                    diff.len(),
                    level_examples.len(),
                    level_new_chars.len()
                );
                if !level_examples.is_empty() {
                    assert!(!level_new_chars.is_empty());
                    remainder = gen_level(
                        batches,
                        level,
                        &level_new_chars,
                        &done,
                        level_examples,
                        remainder,
                    );
                    advanced = true;
                    break;
                }
            }
        }
        if let Some(r) = &remainder {
            assert!(r.examples.len() <= 20);
        }

        if advanced && batches.len() == len_before && remainder == remainder_before {
            // restart level with new rng
            let last_level = batches.last().unwrap().level.to_string();
            println!("RESTARTING LEVEL {}, hopefully new RNG", last_level);
            while batches
                .last()
                .map(|x| x.level == last_level)
                .unwrap_or(false)
            {
                batches.pop();
                remainder = None;
            }
        } else if !advanced {
            break;
        }
    }
    if let Some(r) = remainder {
        if batches.len() < target_len {
            batches.push(r);
        }
    }
}

fn gen_level(
    batches: &mut Vec<Batch>,
    level: &str,
    new_chars: &Charset,
    prev_done: &Charset,
    mut examples: Vec<&Example>,
    mut remainder: Option<Batch>,
) -> Option<Batch> {
    examples.shuffle(&mut thread_rng());

    let remainder_chars = remainder.as_ref().map(|x| x.chars.len()).unwrap_or(0);
    println!(
        "Level {}: {} characters using {} examples, remainder has {} chars and {} examples",
        level,
        new_chars.len(),
        examples.len(),
        remainder_chars,
        remainder.as_ref().map(|x| x.examples.len()).unwrap_or(0),
    );

    let avg_len = examples.len() as f32 * CHARS_PER_BATCH as f32 / new_chars.len() as f32;
    let mut batch_count = 0;
    let mut sum_len = 0;

    let mut done = prev_done.union(
        remainder
            .as_ref()
            .map(|x| &x.chars)
            .unwrap_or(&Charset::default()),
    );

    loop {
        println!("iter with {} examples", examples.len());
        let mut batch = remainder.take().unwrap_or_else(|| Batch {
            level: level.to_string(),
            ..Default::default()
        });
        let remaining_chars = new_chars.diff(&done);
        let todo_chars = CHARS_PER_BATCH - batch.chars.len();
        if remaining_chars.len() <= todo_chars {
            for ex in examples.iter() {
                batch.examples.push((*ex).clone());
                batch.chars = batch.chars.union(&ex.chars.diff(&done).inter(&new_chars));
            }
            if batch.chars.len() == CHARS_PER_BATCH {
                println!(
                    "-> all remaining examples sum up to exaclty {} chars",
                    CHARS_PER_BATCH
                );
                batches.push(batch);
                return None;
            } else if batch.examples.is_empty() {
                assert!(batch.chars.is_empty());
                println!("-> done");
                return None;
            } else {
                assert!(batch.chars.len() < CHARS_PER_BATCH);
                println!(
                    "-> with all remaining examples, cannot make a full batch, only {} chars",
                    batch.chars.len()
                );
                return Some(batch);
            }
        }
        assert!(!examples.is_empty());

        println!(
            "Trying to add exactly {} characters, using {} examples containing {} new chars",
            todo_chars,
            examples.len(),
            remaining_chars.len()
        );

        // Compute dynamic algorithm matrix with a bunch of combinations that add `todo_chars`
        let mut dyn_mat: Vec<Vec<Option<(Charset, Option<(usize, usize)>)>>> = vec![];
        for ex in examples.iter() {
            let mut dyn_row = vec![None; todo_chars + 1];
            let chars_common = ex.chars.inter(&new_chars).diff(&done);
            if chars_common.len() > MAX_NEW_CHARS_PER_EX {
                dyn_mat.push(dyn_row);
                continue;
            }
            if chars_common.len() < dyn_row.len() {
                dyn_row[chars_common.len()] = Some((chars_common.clone(), None));
            }
            for (i, dyn_prev) in dyn_mat.iter().enumerate() {
                for (j, dpr) in dyn_prev.iter().enumerate() {
                    if let Some((chars_inter, _prev)) = dpr {
                        assert_eq!(chars_inter.len(), j);
                        let new_chars_common = chars_inter.union(&chars_common);
                        let new_chars_common_len = new_chars_common.len();
                        if new_chars_common_len > chars_inter.len()
                            && new_chars_common_len <= todo_chars
                        {
                            dyn_row[new_chars_common_len] = Some((new_chars_common, Some((i, j))));
                        }
                    }
                }
            }
            dyn_mat.push(dyn_row);
        }

        // Find combination that does that with a good number of examples (tgt_len)
        let tgt_len = (avg_len * (batch_count as f32 + 1.)).ceil() as i64
            - (sum_len + batch.examples.len()) as i64;
        let dyn_mat_cnt = |i| {
            let mut cnt = 0;
            let mut i: usize = i;
            let mut j: usize = todo_chars;
            loop {
                match &dyn_mat[i][j] {
                    None => return None,
                    Some((_, ij_prev)) => {
                        cnt += 1;
                        match ij_prev {
                            Some((iprev, jprev)) => {
                                i = *iprev;
                                j = *jprev;
                            }
                            None => return Some(cnt),
                        }
                    }
                }
            }
        };
        let i_opt = (0..dyn_mat.len())
            .filter_map(|pos| dyn_mat_cnt(pos).map(|cnt| (pos, cnt)))
            .min_by_key(|(_, cnt)| {
                let x = *cnt as i64 - tgt_len;
                x * x
            });
        let i = match i_opt {
            None => {
                println!(
                    "WARNING: cannot make exactly {} chars, interrupting",
                    todo_chars
                );
                return None;
            }
            Some((pos, _)) => pos,
        };

        // Take all examples from that combination and add them to current batch
        let (mut i, mut j) = (i, todo_chars);
        loop {
            match &dyn_mat[i][j] {
                None => panic!("dyn_mat[{}][{}] == None", i, j),
                Some((chars, ij_prev)) => {
                    println!(
                        "Add {}: {}",
                        examples[i].chars.inter(&chars).to_string(),
                        examples[i].ja
                    );
                    batch.examples.push(examples[i].clone());
                    examples.remove(i);
                    batch.chars = batch.chars.union(&chars);
                    match ij_prev {
                        Some((iprev, jprev)) => {
                            assert!(*iprev < i);
                            i = *iprev;
                            j = *jprev;
                        }
                        None => break,
                    }
                }
            }
        }
        assert_eq!(batch.chars.len(), CHARS_PER_BATCH);

        println!(
            "-> batch {:03}: {} with {} examples",
            batches.len(),
            batch.chars.to_string(),
            batch.examples.len()
        );
        batch_count += 1;
        done = done.union(&batch.chars);
        sum_len += batch.examples.len();
        batches.push(batch);
    }
}

fn level_examples<'a>(
    chars: &Charset,
    avoid: &Charset,
    all_examples: &'a [Example],
) -> Vec<&'a Example> {
    println!("Calculating examples for {}", chars.to_string());

    let mut todo = chars.clone();
    let mut bad = Charset::default();
    let mut examples = vec![];

    let cost = |ex: &Example, ex_todo_inter: usize, ex_chars_inter: usize| {
        (
            -(ex.chars.inter_len(&avoid) as i32),
            ex_todo_inter,
            ex_chars_inter,
            -(ex.ja.chars().count() as i32),
            ex.chars.len() + thread_rng().gen_range(0..5),
        )
    };
    let mut all_with_inter = all_examples
        .par_iter()
        .map(|ex| (ex, ex.chars.inter_len(&chars)))
        .map(|(ex, ex_chars_inter)| (ex, ex_chars_inter, ex_chars_inter))
        .collect::<Vec<_>>();

    while !todo.is_empty() {
        let best = all_with_inter
            .par_iter()
            .enumerate()
            .filter(|(_, (_, ex_todo_inter, _))| *ex_todo_inter > 0)
            //.filter(|(_, (_, _, ex_tgt_inter))| (1..=8).contains(ex_tgt_inter))
            .max_by_key(|(_, (ex, ex_todo_inter, ex_chars_inter))| {
                cost(*ex, *ex_todo_inter, *ex_chars_inter)
            });
        if let Some((i, (ex, ex_todo_inter, _))) = best {
            let ex = *ex;
            assert_eq!(*ex_todo_inter, ex.chars.inter(&todo).len());
            examples.push(ex);
            all_with_inter.remove(i);
            todo = todo.diff(&ex.chars);
            bad = bad.union(&ex.chars.inter(&avoid));
            all_with_inter
                .par_iter_mut()
                .for_each(|(ex2, ex_todo_inter, _)| {
                    if ex2.chars.inter_len(&ex.chars) > 0 {
                        *ex_todo_inter = ex2.chars.inter_len(&todo);
                    }
                });
        } else {
            break;
        }
    }
    if !todo.is_empty() {
        println!("MISSING: NO SENTENCES FOR {}", todo.to_string());
    }
    if !bad.is_empty() {
        println!("USED BAD CHARS: {}", bad.to_string());
    }
    examples
}

fn simplify_batch(batch: &mut Batch) {
    let mut char_cnt = HashMap::<char, usize>::new();
    for ex in batch.examples.iter() {
        for ch in batch.chars.inter(&ex.chars).chars() {
            *char_cnt.entry(*ch).or_default() += 1;
        }
    }

    loop {
        let i_opt = batch.examples.iter().position(|ex| {
            batch
                .chars
                .inter(&ex.chars)
                .chars()
                .iter()
                .all(|x| char_cnt[x] >= 2)
        });
        if let Some(i) = i_opt {
            println!(
                "Removing {} [{}]",
                batch.examples[i].ja,
                batch.examples[i].chars.to_string()
            );
            batch.examples.remove(i);
        } else {
            break;
        }
    }
}

fn cleanup_batches(all_batches: &mut [Batch], kanji_levels: &[(String, Charset)]) {
    let mut chars_p1 = Charset::default();
    let mut chars_p2 = Charset::default();
    let mut done = Charset::default();

    for batch in all_batches.iter_mut() {
        let all_chars = Charset::from_iter(
            batch
                .examples
                .iter()
                .map(|x| x.chars.chars().iter().copied())
                .flatten(),
        );

        let mut levels = kanji_levels
            .iter()
            .filter(|(_, chars)| chars.inter_len(&batch.chars) > 0)
            .map(|(lvl, _)| lvl.to_string())
            .collect::<Vec<_>>();
        while levels.len() > 2 {
            levels.remove(1);
        }
        batch.level = levels.join("/");
        done = done.union(&batch.chars);
        batch.chars_bad = all_chars.diff(&done);
        batch.chars_p1 = all_chars.inter(&chars_p1);
        batch.chars_p2 = all_chars.inter(&chars_p2);

        chars_p2 = chars_p1;
        chars_p1 = batch.chars.clone();
    }
}

fn add_vocab(all_batches: &mut [Batch], vocab: &[JlptVocab]) {
    let match_level = |batch: &Batch, level: &str| {
        let n5 = batch.level.contains("N5");
        let n4 = batch.level.contains("N4");
        let n3 = batch.level.contains("N3");
        let n2 = batch.level.contains("N2");
        let n1 = batch.level.contains("N1");
        let n0 = batch.level.contains("N0");
        match level {
            "N5" => n5 || n4 || n3 || n2 || n1 || n0,
            "N4" => n4 || n3 || n2 || n1 || n0,
            "N3" => n3 || n2 || n1 || n0,
            "N2" => n2 || n1 || n0,
            "N1" => n1 || n0,
            "N0" => n0,
            _ => panic!("invalid vocab level {}", level),
        }
    };

    let mut done = Charset::default();
    let mut extra_vocab = vec![];
    for (i, batch) in all_batches.iter().enumerate() {
        let done_after = done.union(&batch.chars);

        let batch_extra_vocab = vocab
            .iter()
            .filter(|v| v.chars.inter_len(&batch.chars) > 0)
            .filter(|v| match_level(batch, &v.level))
            .filter(|v| v.chars.diff(&done_after).len() == 0)
            .filter(|v| {
                !all_batches[i..std::cmp::min(all_batches.len(), i + 10)]
                    .iter()
                    .any(|b| {
                        b.examples
                            .iter()
                            .any(|ex| ex.ja.contains(&v.kanji) || ex.expl.contains(&v.kanji))
                    })
            })
            .cloned()
            .collect::<Vec<_>>();
        extra_vocab.push(batch_extra_vocab);

        println!("---- BATCH #{:03} ----", i);
        for v in batch.extra_vocab.iter() {
            println!("{}", v.to_string());
        }

        done = done_after;
    }

    for (batch, vocab) in all_batches.iter_mut().zip(extra_vocab.into_iter()) {
        batch.extra_vocab = vocab;
    }
}

fn add_extra_examples(all_batches: &mut [Batch], examples: &[Example]) {
    let mut chars = Charset::default();
    let mut char_seen_count: HashMap<char, usize> = HashMap::new();

    for (i, batch) in all_batches.iter_mut().enumerate() {
        println!("---- BATCH #{:03} ----", i);
        chars = chars.union(&batch.chars);

        // Count characters in batch in char_seen_count as a lot
        for ex in batch.examples.iter() {
            for c in ex.chars.iter() {
                *char_seen_count.entry(c).or_default() += 5;
            }
        }

        // Take only examples that:
        // - contain kanji of this batch
        // - only contain kanji of this or previous batches
        // - are not in the batch's main example sentences
        let candidates = examples
            .iter()
            .filter(|x| x.chars.inter_len(&batch.chars) > 0)
            .filter(|x| x.chars.diff(&chars).len() == 0)
            .filter(|x| batch.examples.iter().all(|y| y.ja != x.ja));

        // Take only one candidate sentence for each possible set of represented kanji
        let mut cand_by_chars = HashMap::new();
        for c in candidates {
            cand_by_chars.insert(c.chars.to_string(), c.clone());
        }
        let mut candidates = cand_by_chars
            .into_iter()
            .map(|(_, ex)| ex)
            .collect::<Vec<_>>();

        // Sorte candidates in a deterministic random order
        candidates.sort_by_key(|ex| fasthash::metro::hash64(ex.ja.as_bytes()));

        batch.extra_examples.clear();

        let mut batch_char_seen_count: HashMap<char, usize> = HashMap::new();
        let mut in_batch =
            Charset::from_iter(batch.examples.iter().map(|x| x.chars.iter()).flatten());
        let mut in_batch_extra = Charset::default();

        while batch.extra_examples.len() < 40 {
            let batch_min_seen = batch
                .chars
                .iter()
                .map(|x| batch_char_seen_count.get(&x).copied().unwrap_or(0))
                .min()
                .unwrap();
            // Target chars: chars of the batch that have the less examples
            let c0 =
                Charset::from_iter(batch.chars.iter().filter(|x| {
                    batch_char_seen_count.get(x).copied().unwrap_or(0) == batch_min_seen
                }));
            // Target chars: chars that have been seen less than cnt times
            let fc = |cnt| {
                Charset::from_iter(
                    chars
                        .iter()
                        .filter(|x| char_seen_count.get(x).copied().unwrap_or(0) <= cnt),
                )
            };
            let c1 = fc(5);
            let c2 = fc(6);
            let c3 = fc(7);
            let c4 = fc(10);

            let best = candidates
                .iter()
                .enumerate()
                .filter(|(_, ex)| {
                    batch.extra_examples.len() < 20 || ex.chars.diff(&in_batch_extra).len() > 0
                })
                .map(|(i, ex)| {
                    let weight = (
                        ex.chars.inter_len(&c0),
                        ex.chars.inter_len(&c1),
                        ex.chars.inter_len(&c2),
                        ex.chars.inter_len(&c3),
                        ex.chars.inter_len(&c4),
                        ex.chars.diff(&in_batch_extra).len(),
                    );
                    (i, ex, weight)
                })
                .max_by_key(|(_, _, w)| *w);
            if let Some((i, ex, w)) = best {
                println!("{:?}\t{} - {}", w, ex.ja, ex.en);

                batch.extra_examples.push(ex.clone());
                in_batch = in_batch.union(&ex.chars);
                in_batch_extra = in_batch_extra.union(&ex.chars);

                for c in ex.chars.iter() {
                    *char_seen_count.entry(c).or_default() += 1;
                    if batch.chars.contains(c) {
                        *batch_char_seen_count.entry(c).or_default() += 1;
                    }
                }

                candidates.remove(i);
            } else {
                break;
            }
        }

        batch
            .extra_examples
            .sort_by_key(|ex| fasthash::metro::hash64(ex.ja.as_bytes()));

        for i in 1..20 {
            println!(
                "Seen   {:02}: {}",
                i,
                char_seen_count.iter().filter(|(_, v)| **v == i).count()
            );
        }
        println!(
            "Seen more: {}",
            char_seen_count.iter().filter(|(_, v)| **v >= 20).count()
        );
    }
}