CodeWars/5kyu/tic_tac_toe_checker/solution.js

function checkEmpty(board) {
    for (let i = 0; i < 3; i++) {
        for (let j = 0; j < 3; j++) {
            if (board[i][j] === 0) {
                return true;
            }
        }
    }
}

function checkColumn(board, column) {
    for (let i = 1; i < 3; i++) {
        if (board[i - 1][column] !== board[i][column]) {
            return 0;
        }
    }
    return board[0][column];
}

function checkRow(board, row) {
    for (let i = 1; i < 3; i++) {
        if (board[row][i - 1] !== board[row][i]) {
            return 0;
        }
    }
    return board[row][0];
}

function checkDiagonal(board) {
    let leftToRight = true;
    let rightToLeft = true;
    for (let i = 1; i < 3; i++) {
        if (board[i - 1][i - 1] !== board[i][i]) {
            leftToRight = false;
        }
        if (board[i - 1][3 - i] !== board[i][2 - i]) {
            rightToLeft = false;
        }
    }

    if (leftToRight) {
        return board[0][0];
    } else if (rightToLeft) {
        return board[0][2];
    } else {
        return 0;
    }
}

function isSolved(board) {
    for (let i = 0; i < 3; i++) {
        const col = checkColumn(board, i);
        const row = checkRow(board, i);
        if (col != 0) {
            return col;
        } else if (row != 0) {
            return row;
        }
    }

    const diagonal = checkDiagonal(board);
    if (diagonal != 0) {
        return diagonal;
    }

    if (checkEmpty(board)) {
        return -1;
    }

    return 0;
}