按照y总的思路一稍作修改后运行时间与思路二相同

C++ 代码

#include <iostream>

using namespace std;

const int N = 20;

int n;
char g[N][N];
bool row[N], col[N], dg[N], udg[N];

void dfs(int u, int v)
{
    if (u >= n) 
    {
        for (int i = 0; i < n; i ++ ) puts(g[i]);
        puts("");
        return;
    }

    if (v == n) return;

    g[u][v] = '.';

    dfs(u, v + 1);

    g[u][v] = '\0';

    if (!col[v] && !dg[u + v] && !udg[n - u + v])
    {
        g[u][v] = 'Q';
        row[v] = col[v] = dg[u + v] = udg[n - u + v] = true;
        for (int i = v + 1; i < n; i ++ ) g[u][i] = '.';

        dfs(u + 1, 0);

        for (int i = v + 1; i < n; i ++ ) g[u][i] = '\0';
        row[v] = col[v] = dg[u + v] = udg[n - u + v] = false;
        g[u][v] = '.';
    }

}

int main()
{
    cin >> n;

    dfs(0, 0);

    return 0;
}