use std::{char, collections::HashMap};

pub fn word_search(board: &[Vec<char>], words: &[&str]) -> Vec<String> {
    let mut first_char_to_word = HashMap::new();
    for w in words {
        first_char_to_word
            .entry(w.chars().next().unwrap())
            .or_insert(vec![])
            .push(w);
    }

    let mut result = Vec::new();

    for (rown, row) in board.iter().enumerate() {
        for (column, ch) in row.iter().enumerate() {
            if let Some(possible_words) = first_char_to_word.get(ch) {
                for word in possible_words {
                    if search(
                        rown,
                        column,
                        board,
                        &word.chars().skip(1).collect::<Vec<char>>(),
                    ) {
                        result.push(word.to_owned().to_owned().to_owned());
                    }
                }
            }
        }
    }

    result
}

fn search(row: usize, column: usize, board: &[Vec<char>], word: &[char]) -> bool {
    if word.is_empty() {
        return true;
    }
    let (first_char, other_chars) = word.split_first().unwrap();

    if row > 0 {
        if let Some(char_row) = board.get(row - 1) {
            if char_row.get(column).unwrap() == first_char
                && search(row - 1, column, board, other_chars)
            {
                return true;
            }
        }
    }
    if let Some(char_row) = board.get(row + 1) {
        if char_row.get(column).unwrap() == first_char
            && search(row + 1, column, board, other_chars)
        {
            return true;
        }
    }
    if let Some(char_row) = board.get(row) {
        if column > 0
            && char_row.get(column - 1).unwrap() == first_char
            && search(row, column - 1, board, other_chars)
        {
            return true;
        }
        if column + 1 < char_row.len()
            && char_row.get(column + 1).unwrap() == first_char
            && search(row, column + 1, board, other_chars)
        {
            return true;
        }
    }

    false
}