37. 解数独（算法200题-85）

var solveSudoku = function (board) {
    for (let row = 0; row < 9; row++) {
        for (let col = 0; col < 9; col++) {
            if (board[row][col] !== '.') continue
            for (let num = 1; num < 10; num++) {
                const isSet = cheackSet(row, col, board, num + '')
                if (!isSet) continue
                board[row][col] = num + ''
                // 判断是否能继续进行
                if (solveSudoku(board)) return true
                // 回退
                board[row][col] = '.'
            }
            // 当前格子没有不符合的，则回退
            return false
        }
    }
    return true
};
// 检查是否满足题意
function cheackSet(row, col, board, num) {
    for (let i = 0; i < 9; i++) {
        if (board[i][col] === num || board[row][i] === num) {
            return false
        }
    }
    return checkIn33(row, col, board, num)
}
function checkIn33(row, col, board, num) {
    const x = Math.floor(row / 3) * 3
    const y = Math.floor(col / 3) * 3
    for (let i = x; i < x + 3; i++) {
        for (let j = y; j < y + 3; j++) {
            if (board[i][j] === num) {
                return false
            }
        }
    }
    return true
}