solution.js

/**
 * @param {string[]} board
 * @return {string}
 */
var tictactoe = function (board) {
    const N = board.length;
    if (N === 1) {
        if (board[0][0] === ' ') {
            return 'Pending';
        } else {
            return 'O';
        }
    }
    const colMatch = new Array(N).fill(true);
    let hasRest = false;
    for (let i = 0; i < N; i++) {
        let rowMatch = true;
        for (let j = 0; j < N; j++) {
            if (board[i][j] === ' ') {
                hasRest = true;
                colMatch[j] = false;
                rowMatch = false;
                continue;
            }
            if (j > 0 && rowMatch && board[i][j] !== board[i][0]) {
                rowMatch = false;
            }
            if (i > 0 && colMatch[j] && board[i][j] !== board[0][j]) {
                colMatch[j] = false;
            }
        }

        if (rowMatch) {
            return board[i][0];
        }
    }

    for (let j = 0; j < N; j++) {
        if (colMatch[j]) {
            return board[0][j];
        }
    }
    let diagonal1 = board[0][0] !== ' ';
    let diagonal2 = board[0][N - 1] !== ' ';
    for (let i = 1; i < N; i++) {
        if (diagonal1 && board[i][i] !== board[0][0]) {
            diagonal1 = false;
        }
        if (diagonal2 && board[i][N - i - 1] !== board[0][N - 1]) {
            diagonal2 = false;
        }
    }
    if (diagonal1) {
        return board[0][0];
    }
    if (diagonal2) {
        return board[0][N - 1];
    }
    if (hasRest) {
        return 'Pending';
    }
    return 'Draw';
};