一、题目
The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.
Given an integer n, return all distinct solutions to the n-queens puzzle. You may return the answer in any order.
Each solution contains a distinct board configuration of the n-queens’ placement, where ‘Q’ and ‘.’ both indicate a queen and an empty space, respectively.
Input: n = 4
Output: [[“.Q…”,“…Q”,“Q…”,“…Q.”],[“…Q.”,“Q…”,“…Q”,“.Q…”]]
Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above
Example 2:
Input: n = 1
Output: [[“Q”]]
1 <= n <= 9
二、题解
class Solution {
public:
vector<vector<string>> res;
bool isValid(vector<string>& chessboard,int row,int col,int n){
//检查列
for(int i = 0;i < row;i++){
if(chessboard[i][col] == 'Q') return false;
}
//检查45度角
for(int i = row - 1,j = col - 1;i >= 0 && j >= 0;i--,j--){
if(chessboard[i][j] == 'Q') return false;
}
//检查135度角
for(int i = row - 1,j = col + 1;i >= 0 && j < n;i--,j++){
if(chessboard[i][j] == 'Q') return false;
}
return true;
}
void backtracing(vector<string>& chessboard,int row,int n){
if(row == n){
res.push_back(chessboard);
return;
}
for(int i = 0;i < n;i++){
if(isValid(chessboard,row,i,n)){
chessboard[row][i] = 'Q';
backtracing(chessboard,row+1,n);
chessboard[row][i] = '.';
}
}
}
vector<vector<string>> solveNQueens(int n) {
vector<string> chessboard(n,string(n,'.'));
backtracing(chessboard,0,n);
return res;
}
};
原文地址:https://blog.csdn.net/weixin_46841376/article/details/134640427
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