代码：

#include <iostream>using namespace std;const int N = 20;int n;
char g[N][N];
bool col[N], dg[N], udg[N];void dfs(int u)
{if(u == n){for(int i = 0; i < n; i++) puts(g[i]);puts("");return;                }for(int i = 0; i < n; i++)if(!col[i] && !dg[u + i] && !udg[n - u + i]){g[u][i] = 'Q';col[i] = dg[u + i] = udg[n - u + i] = true;dfs(u + 1);col[i] = dg[u + i] = udg[n - u + i] = false;g[u][i] = '.';       }
}int main()
{cin >> n;for(int i = 0; i < n; i++)for(int j = 0; j < n; j++)g[i][j] = '.';dfs(0);return 0;
}