HDU3342拓扑排序

方法一： 
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<map>
#include<queue>
#include<set>
#include<vector>
using namespace std;
typedef long long ll;
const int maxx=105;
int n,m;
int indegree[maxx];
int a[maxx];
vector<int>ans[maxx];
int k;
void Topsort(int n){
	int index;
	int m=0;
	for(int i=0;i<n;i++){
		m=0;
		for(int j=0;j<n;j++){
			if(indegree[j]==0){
				index=j;
				m++;
			}
		}
		if(m==0)break;
		a[++k]=index;
		indegree[index]=-1;
		for(int j=0;j<ans[index].size();j++){
			int t=ans[index][j];
			indegree[t]--;
		}
	}
}
int main(){
	while(scanf("%d %d",&n,&m)){
		if(n==0&&m==0)break;
		memset(indegree,0,sizeof(indegree));
		memset(a,0,sizeof(a));
		for(int i=0;i<=n;i++){
			ans[i].clear();
		}
		for(int i=1;i<=m;i++){
			int x,y;
			scanf("%d %d",&x,&y);
			ans[x].push_back(y);
			indegree[y]++;
		}
		k=0;
		Topsort(n);
		if(k==n){
			cout<<"YES"<<endl;
		}else{
			cout<<"NO"<<endl;
		}
	}
	return 0;
} 
方法二： 
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#include<map>
#include<queue>
using namespace std;
const int maxx=1e3+10;
int vis[maxx][maxx];
int indegree[maxx];
int n,m;
vector<int>ans[maxx];
int a[maxx];
int main(){
	while(scanf("%d %d",&n,&m)!=EOF){
		if(n==0&&m==0)break;
		memset(indegree,0,sizeof(indegree));
		memset(vis,0,sizeof(vis));
		for(int i=0;i<=n;i++){
			ans[i].clear();
		}
		for(int i=1;i<=m;i++){
			int x,y;
			scanf("%d %d",&x,&y);
			ans[x].push_back(y);
			indegree[y]++;
		}
		queue<int>q;
		for(int i=0;i<n;i++){
			if(indegree[i]==0){
				q.push(i);
			}
		}
		int k=0;
		while(!q.empty()){
			int u=q.front();
			q.pop();
			a[++k]=u;
			for(int i=0;i<ans[u].size();i++){
				int t=ans[u][i];
				indegree[t]--;
				if(indegree[t]==0){
					q.push(t);
				}
			}
		}
		if(k==n){
			cout<<"YES"<<endl; 
		}else{
			cout<<"NO"<<endl;
		}
	}
	return 0;
}