pku2762(Going from u to v or from v to u?)

/*
* File: pku2762.cpp,判断是否为若联通图，缩点后构建新图，对新图进行拓扑排序，
* 如果拓扑序列唯一，则为若联通图
* Author: chenjiang
*
* Created on 2010年5月8日, 下午4:05
*/

#include <stdlib.h>
#include <iostream>
#include <string.h>
#include <stdio.h>
#include <vector>
#include <queue>
using namespace std;
#define _max 1001
vector<int>v1[_max];
vector<int>v2[_max];
vector<int>v3[_max];
bool visited[_max];
int scc_id[_max];
int order[_max];
int indegree[_max];
int n, m;
int id;
int ind;

void dfs1(int k) {
int i;
visited[k] = 1;
for (i = 0; i < v1[k].size(); i++) {
if (!visited[v1[k][i]])
dfs1(v1[k][i]);
}
ind++;
order[ind] = k;
}

void dfs2(int k) {
int i;
visited[k] = 1;
scc_id[k] = id;
for (i = 0; i < v2[k].size(); i++) {
if (!visited[v2[k][i]])
dfs2(v2[k][i]);
}
}

void kosaroju() {
int i;
ind = 0;
memset(visited, 0, sizeof (visited));
for (i = 1; i <= n; i++) {
if (!visited[i])
dfs1(i);
}

memset(visited, 0, sizeof (visited));
id = 0;
for (i = ind; i >= 1; i--) {
if (!visited[order[i]]) {
id++;
dfs2(order[i]);
}
}
}

bool top_sort() {//判断拓扑序列是否唯一
int i,j;
int k;
int num=0;
for(i=1;i<=id;i++)
{
num=0;
for(j=1;j<=id;j++)
{
if(indegree[j]==0)
{
k=j;
num++;
}
}
//if(num==0)return 0;
if(num>1)return 0;
indegree[k]=-1;
for(j=0;j<v3[k].size();j++)
{
indegree[v3[k][j]]--;
}
}
return 1;
}

/*
*
*/
int main(int argc, char** argv) {

int i, j, a, b;
int t;
//freopen("a.a", "r", stdin);
cin >> t;
while (t--) {
cin >> n >> m;
for (i = 1; i <= n; i++) {
v1[i].clear();
v2[i].clear();
v3[i].clear();
}
for (i = 1; i <= m; i++) {
cin >> a >> b;
v1[a].push_back(b);
v2[b].push_back(a);
}
kosaroju();/*
cout << id << endl;
for (i = 1; i <= n; i++) {
printf("scc_id[%d]=%d/n", i, scc_id[i]);
}*/
memset(indegree, 0, sizeof (indegree));
for (i = 1; i <= n; i++) {
for (j = 0; j < v1[i].size(); j++) {
if (scc_id[i] != scc_id[v1[i][j]]) {
v3[scc_id[i]].push_back(scc_id[v1[i][j]]);
indegree[scc_id[v1[i][j]]]++;
}
}
}/*
for (i = 1; i <= id; i++) {
printf("indegree[%d]=%d/n", i, indegree[i]);
}*/
int ans = top_sort();//cout<<"top_sort over"<<endl;
if (ans)cout << "Yes" << endl;
else cout << "No" << endl;
//system("pause");
}
return (EXIT_SUCCESS);
}