https://leetcode.com/problems/n-queens-ii/

解法跟 N-queen 一模一样…

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
/**
 * @param {number} n
 * @return {number}
 */
const totalNQueens = function(n) {
    let res = []
    let board = []
    for (let i = 0; i < n; i++) {
        board.push('.'.repeat(n))
    }
    backtrack(n, res, board)
    return res.length
}

const backtrack = function(n, res, board = [], row = 0) {
    if (row === n) {
        return res.push([...board]) // attention
    }
    for (let col = 0; col < n; col++) { // attention
        if (isValid(board, row, col, n)) {
            board[row] = board[row].substr(0, col) + 'Q' + board[row].substr(col + 1)
            backtrack(n, res, board, row + 1)
            board[row] = board[row].substr(0, col) + '.' + board[row].substr(col + 1)
        }
    }
}

const isValid = function(board, r, c, n) {
    for (let i = 0; i < r; i++) {
        if (board[i][c] === 'Q') {
            return false
        }
    }
    for (let i = r - 1, j = c - 1; i >= 0 && j >= 0; i--, j--) {
        if (board[i][j] === 'Q') {
            return false
        }
    }
    for (let i = r - 1, j = c + 1; i >= 0 && j < n; i--, j++) { // attention
        if (board[i][j] === 'Q') {
            return false
        }
    }
    return true
}