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export default function exist(board: string[][], word: string): boolean {    if (        word.length === 1 &&        board.length === 1 &&        board[0].length === 1 &&        word === board[0][0]    ) {        return true;    }    if (word.length === 0) return false;    const row = board.length;    if (!row) return false;    const col = board[0].length;    if (!col) return false;
    const first = word[0];
    const visited: boolean[][] = Array.from(board).map((a) =>        Array.from(a).map(() => false)    );    // console.log(starts)    const directions: Array<[number, number]> = [        [0, 1],        [1, 0],        [0, -1],        [-1, 0],    ];    function dfs(word: string, i: number, j: number): boolean {        // console.log({ word, i, j })        // console.log(visited)        if (board[i][j] !== word[0]) return false;        else if (word.length === 1) return true;
        visited[i][j] = true;        // let result = false        for (const [f, s] of directions) {            const x = i + f;            const y = j + s;            if (x >= 0 && y >= 0 && x < row && y < col) {                if (!visited[x][y]) {                    if (dfs(word.slice(1), x, y)) {                        visited[i][j] = false;                        return true;                    } /* else {
              // visited[x][y] = false              //visited[i][j] = false;            } */                }            }        }        visited[i][j] = false;        return false;    }
    const all_chars = new Set(board.flat());
    if (Array.prototype.some.call(word, (c) => !all_chars.has(c))) return false;    for (let i = 0; i < row; i++) {        for (let j = 0; j < col; j++) {            if (first === board[i][j]) {                const flag = dfs(word, i, j);                if (flag) {                    return true;                }            }        }    }    return false;}