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  • hdu3594 Cactus

    仙人掌入门简单题。
    先看一篇文档

    #include <iostream>
    #include <cstring>
    #include <cstdio>
    using namespace std;
    int T, n, uu, vv, hea[20005], cnt, dfn[20005], loo[20005], idx, vis[20005];
    bool isok;
    struct Edge{
    	int too, nxt;
    }edge[50005];
    void add_edge(int fro, int too){
    	edge[++cnt].nxt = hea[fro];
    	edge[cnt].too = too;
    	hea[fro] = cnt;
    }
    void dfs(int x){
    	if(!isok)	return ;
    	dfn[x] = loo[x] = ++idx;
    	vis[x] = 1;
    	int num=0;
    	for(int i=hea[x]; i; i=edge[i].nxt){
    		int t=edge[i].too;
    		if(vis[t]==2)	isok = false;//1
    		else if(!vis[t]){
    			dfs(t);
    			if(loo[t]>dfn[x])	isok = false;//2
    			if(loo[t]<dfn[x]){//3
    				num++;
    				loo[x] = min(loo[x], loo[t]);
    			}
    		}
    		else{//3
    			loo[x] = min(loo[x], dfn[t]);
    			num++;
    		}
    	}
    	vis[x] = 2;
    	if(num>1)	isok = false;
    }
    int main(){
    	cin>>T;
    	while(T--){
    		scanf("%d", &n);
    		memset(dfn, 0, sizeof(dfn));
    		memset(loo, 0, sizeof(loo));
    		memset(hea, 0, sizeof(hea));
    		memset(vis, 0, sizeof(vis));
    		isok = true;
    		cnt = idx = 0;
    		while(scanf("%d %d", &uu, &vv)!=EOF){
    			if(!uu && !vv)	break;
    			add_edge(uu+1, vv+1);
    		}
    		dfs(1);
    		if(idx<n)	isok = false;
    		printf(isok?"YES
    ":"NO
    ");
    	}
    	return 0;
    }
    
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  • 原文地址:https://www.cnblogs.com/poorpool/p/8587088.html
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