hdu 4324 Triangle LOVE

先进行拓扑排序，删除那些不会成环的节点。剩下的节点再重建一张图，进行DFS。

#include<cstdio>

#include<cstring>

#include<cmath>

#include<string>

#include<vector>

#include<algorithm>

using namespace std;



const int maxn = 2000 + 5;

int jz[maxn][maxn], rudu[maxn], flag[maxn];

vector<int>ljb[maxn];

int uu;

char s[2005];



void dfs(int tott, int now,int tou)

{

    int i;

    if (tott == 2)

    {

        if (jz[now][tou] == 1) uu = 1;

        return;

    }

    for (i = 0; i < ljb[now].size(); i++)

    {

        dfs(tott + 1, ljb[now][i], tou);

        if (uu == 1) return;

    }

}



int main()

{

    int sb, bs;

    scanf("%d", &sb);

    for (bs = 1; bs <= sb; bs++)

    {

        int n, i, j; uu = 0;

        scanf("%d", &n);

        for (i = 0; i <= n; i++) ljb[i].clear();

        memset(rudu, 0, sizeof(rudu));

        memset(flag, 0, sizeof(flag));

        for (i = 1; i <= n; i++)

        {

            scanf("%s", s);

            for (j = 1; j <= n; j++)

            {

                jz[i][j] = s[j - 1] - '0';

                if (jz[i][j] == 1)

                {

                    ljb[i].push_back(j);

                    rudu[j]++;

                }

            }

        }



        int ff;

        while (1)

        {

            ff = 0;

            for (i = 1; i <= n; i++)

            {

                if (rudu[i] == 0)

                {

                    ff = 1;

                    rudu[i]--;

                    for (j = 0; j < ljb[i].size(); j++)

                        rudu[ljb[i][j]]--;

                }

            }

            if (ff == 0) break;

        }

        for (i = 1; i <= n; i++) if (rudu[i]>0) flag[i] = 1;

        for (i = 0; i <= n; i++) ljb[i].clear();

        for (i = 1; i <= n; i++)

        {

            for (j = 1; j <= n; j++)

            {

                if (jz[i][j] == 1 && flag[i] == 1 && flag[j] == 1)

                {

                    ljb[i].push_back(j);

                }

            }

        }

        for (i = 1; i <= n; i++)

        {

            if (flag[i] == 1)

            {

                uu = 0;

                dfs(0, i, i);

                if (uu == 1) break;

            }

        }

        printf("Case #%d: ", bs);

        if (uu == 1) printf("Yes\n");

        else printf("No\n");

    }

    return 0;

}