记录编号	583575	评测结果	AAAAAAAAAA
题目名称	[POJ 2762]从u到v还是从v到u？	最终得分	100
用户昵称	┭┮﹏┭┮	是否通过	通过
代码语言	C++	运行时间	0.000 s
提交时间	2023-10-18 20:32:34	内存使用	0.00 MiB

#include <bits/stdc++.h>
using namespace std;
const int N = 1e3+10,M = 6e3+10;
//tarjan求强连通分量 +缩点+拓扑序遍历 
int t,n,m;
struct made{
    int ver,nx;
}e[M],re[M];
int hd[N],rhd[N],tot,num,cnt,top;
int low[N],dfn[N],st[N],color[N];
int v[N];//vr为入度，vc为出度
map<pair<int,int>,int>mp; 
void first(){
    tot = cnt = top = num = 0;
    memset(e,0,sizeof(e));
    memset(re,0,sizeof(re));
    memset(hd,0,sizeof(hd));
    memset(rhd,0,sizeof(rhd));
    memset(low,0,sizeof(low));
    memset(dfn,0,sizeof(dfn));
    memset(st,0,sizeof(st));
    memset(color,0,sizeof(color));
    memset(v,0,sizeof(v));
}//初始化:( 
void add(int x,int y){
    tot++;
    e[tot].ver = y,e[tot].nx = hd[x],hd[x] = tot;
}
void radd(int x,int y){
    tot++;
    re[tot].ver = y,re[tot].nx = rhd[x],rhd[x] = tot;
}
void tarjan(int x){
    low[x] = dfn[x] = ++cnt;
    st[++top] = x,v[x] = 1;
    for(int i = hd[x];i;i = e[i].nx){
        int y = e[i].ver;
        if(!dfn[y])tarjan(y),low[x] = min(low[x],low[y]);
        else if(v[y])low[x] = min(low[x],dfn[y]);
    }
    if(low[x] == dfn[x]){
        num++;int y = 0;
        do{
            y = st[top--];
            v[y] = 0,color[y] = num;
        }while(x != y);
    }
}
void push(int x){
    for(int i = hd[x];i;i = e[i].nx){
        int y = e[i].ver;
        if(color[x] == color[y])continue;
        v[color[y]]++;
        radd(color[x],color[y]);
    }
}
bool check(){//拓扑序遍历 
    queue<int>q;
    for(int i = 1;i <= num;i++)
        if(!v[i])q.push(i);
    if(q.size() > 1)return 0;
    while(!q.empty()){
        int x = q.front();q.pop();
        for(int i = rhd[x];i;i = re[i].nx){
            int y = re[i].ver;
            if(--v[y] == 0)q.push(y);
        }
        if(q.size() > 1)return 0;
    }
    return 1;
}
int main(){
    freopen("utov.in","r",stdin);
    freopen("utov.out","w",stdout);
    scanf("%d",&t);
    while(t--){
    	first();
        scanf("%d%d",&n,&m);
        for(int i = 1;i <= m;i++){
            int x,y;
            scanf("%d%d",&x,&y);
            add(x,y);
        }
        for(int i = 1;i <= n;i++)
            if(!color[i])tarjan(i);
        memset(v,0,sizeof(v));
        tot = 0;
        for(int i = 1;i <= n;i++)
            push(i);
        if(check())printf("Yes\n");
        else printf("No\n");
    }
    
    return 0;
    
}