DFS 专题 N皇后

DFS 其实会超时的，打表。

# include <cstdio>

# include <cstring>



# define N 10 + 5



int n, ans;

int solu[N];

bool vis[N];



void dfs(int cnt)

{

    if (cnt == n)

    {

        ++ans;

        return ;

    }

    bool ok;

    for (int i = 1; i <= n; ++i) if (vis[i] == false)

    {

        ok = true;

        for (int j = 1; j <= cnt; ++j)

        {

            if ( i+cnt+1 == solu[j]+j ||

                 cnt+1-i == j-solu[j] )     // BUG : i-cnt-1 == j-solu[j]

            {

                ok = false;

                break;

            }

        }

        if (ok)

        {

            vis[i] = true;

            solu[cnt+1] = i, dfs(cnt+1);

            vis[i] = false;

        }

    }

}



void solve(void)

{

    ans = 0;

    memset(vis, false, sizeof(vis));

    dfs(0);

    printf("%d\n", ans);

}



int main()

{

  const int f[] = {0,1,0,0,2,10,4,40,92,352,724};

    while (scanf("%d", &n), n)

        //solve();

        printf("%d\n", f[n]);



    return 0;

}

/**/