LeetCode(51) N-Queens

题目如下：

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

For example,

There exist two distinct solutions to the 4-queens puzzle:

[

[".Q..", // Solution 1

"...Q",

"Q...",

"..Q."],

["..Q.", // Solution 2

"Q...",

"...Q",

".Q.."]

]

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分析如下：

有了前面的N-QueensII, 这道题目就比较好写了。改变一下输出结果就可以了。

我的代码；

//14ms
class Solution {
public:
    
    void swap(int* array, int a ,int b) {
        int tmp  = array[a];
        array[a] = array[b];
        array[b] = tmp;
    }
    
    bool collide(int k, int* array) {
        for (int i = 0; i <k; ++i) {
            //检查array[k] 和 array[k]之前的数有无冲突
            if ((array[k] - k == array[i] - i) ||
                (array[k] + k == array[i] + i))
                return true;
        }
        return false;
    }
    
    void GenQueens(int k, int n, vector<vector<string> > & result_vec, int* array) {
        if (k == n){
            vector<string> each_vec;
            for (int j = 0; j < n; ++j) {
                string s = "";
                for (int h = 0; h < array[j]; ++h) {
                    s = s + ".";
                }
                s = s + "Q";
                for (int h = array[j] + 1; h < n; ++h) {
                    s = s + ".";
                }
                each_vec.push_back(s);
            }
            result_vec.push_back(each_vec);
            return;
        } else {
            for (int i = k; i < n; ++i) {
                swap(array, i, k);
                //如果交换后的当前值引起了冲突，就不进行下一步的dfs
                if(!collide(k, array)) {
                    GenQueens(k+1, n, result_vec, array);
                }
                swap(array, k, i);
            }
        }
    }

    vector<vector<string> > solveNQueens(int n) {
        int* array = new int
;
        vector<vector<string> > result_vec;
        for (int i = 0; i < n; ++i) {
            array[i] = i;
        }
        GenQueens(0, n, result_vec, array);
        delete [] array;
        return result_vec;
    }
};