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
");
        else printf("No
");
    }
    return 0;
}