poj Going from u to v or from v to u? 强联通缩点+拓扑排序（或搜索）

方法一

#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <stack>#include <set>#include <map>#include <string>#include <math.h>#include <stdlib.h>#include <time.h>//#include<bits/stdc++.h>using namespace std;typedef long long ll;const int N=1024;struct Edge{    int s,t;};int n,m,dfn[N],low[N],in[N],id[N],cnt,dep,mp[N][N];vector<Edge>edge;vector<int>g[N];stack<int>st;void Addedge(int u,int v){    Edge tp;    tp.s=u,tp.t=v;    edge.push_back(tp);    g[u].push_back(edge.size()-1);}void dfs(int u){    int v,i,k,mx=dfn[u]=low[u]=dep++;    st.push(u);    for(i=0;i<g[u].size();i++)    {        v=edge[g[u][i]].t;        if(dfn[v]==-1) dfs(v);        if(mx>low[v]) mx=low[v];    }    if(mx<low[u])    {        low[u]=mx;        return ;    }    //printf("%d\n",cnt);    do    {        k=st.top();        st.pop();        id[k]=cnt;        low[k]=n;    }while(k!=u);    cnt++;}void dfs1(int u,int q){    dfn[u]=1;    dep=max(dep,q);    for(int i=0;i<cnt;i++)    {        if(mp[u][i]==1)            dfs1(i,q+1);    }}int main(){    //freopen("in.txt","r",stdin);    //freopen("out.txt","w",stdout);    int _,i,u,v;    scanf("%d",&_);    while(_--)    {        scanf("%d%d",&n,&m);        for(i=0; i<n; i++)            {                g[i].clear();                id[i]=i;            }        edge.clear();        for(i=0; i<m; i++)        {            scanf("%d%d",&u,&v);            Addedge(u-1,v-1);        }        dep=0;        cnt=0;        while(!st.empty()) st.pop();        memset(dfn,0xff,sizeof(dfn));        for(i=0; i<n; i++)        {            if(dfn[i]==-1)                dfs(i);        }        memset(in,0,sizeof(in));        memset(mp,0,sizeof(mp));        for(i=0; i<m; i++)        {            u=id[edge[i].s];            v=id[edge[i].t];            //printf("%d %d\n",u,v);            if(u!=v)            {                in[v]++;                mp[u][v]=1;            }        }        memset(dfn,0,sizeof(dfn));        for(i=0,dep=0;i<cnt;i++)        {            if(dfn[i]==0) dfs1(i,1);        }        if(dep==cnt) printf("Yes\n");        else printf("No\n");    }    return 0;}

方法二

#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <stack>#include <set>#include <map>#include <string>#include <math.h>#include <stdlib.h>#include <time.h>//#include<bits/stdc++.h>using namespace std;typedef long long ll;const int N=1024;struct Edge{    int s,t;};int n,m,dfn[N],low[N],in[N],id[N],cnt,dep,mp[N][N];vector<Edge>edge;vector<int>g[N];stack<int>st;void Addedge(int u,int v){    Edge tp;    tp.s=u,tp.t=v;    edge.push_back(tp);    g[u].push_back(edge.size()-1);}void dfs(int u){    int v,i,k,mx=dfn[u]=low[u]=dep++;    st.push(u);    for(i=0;i<g[u].size();i++)    {        v=edge[g[u][i]].t;        if(dfn[v]==-1) dfs(v);        if(mx>low[v]) mx=low[v];    }    if(mx<low[u])    {        low[u]=mx;        return ;    }    //printf("%d\n",cnt);    do    {        k=st.top();        st.pop();        id[k]=cnt;        low[k]=n;    }while(k!=u);    cnt++;}int topsort(){    int i,u,v,p;    stack<int>S;    for(i=0;i<cnt;i++)    {        //printf("%d\n",in[i]);        if(in[i]==0)            S.push(i);    }    //printf("%d\n",S.size());    p=0;    while(S.size()==1)    {        u=S.top();S.pop();p++;        for(i=0;i<cnt;i++)        {            if(mp[u][i]==1)            {                in[i]--;                if(in[i]==0) S.push(i);            }        }    }    if(p==cnt) return 1;    else return 0;}int main(){    //freopen("in.txt","r",stdin);    //freopen("out.txt","w",stdout);    int _,i,u,v;    scanf("%d",&_);    while(_--)    {        scanf("%d%d",&n,&m);        for(i=0; i<n; i++)            {                g[i].clear();                id[i]=i;            }        edge.clear();        for(i=0; i<m; i++)        {            scanf("%d%d",&u,&v);            Addedge(u-1,v-1);        }        dep=0;        cnt=0;        while(!st.empty()) st.pop();        memset(dfn,0xff,sizeof(dfn));        for(i=0; i<n; i++)        {            if(dfn[i]==-1)                dfs(i);        }        memset(in,0,sizeof(in));        memset(mp,0,sizeof(mp));        for(i=0; i<m; i++)        {            u=id[edge[i].s];            v=id[edge[i].t];            if(u!=v&&!mp[u][v])            {                in[v]++;                mp[u][v]=1;            }        }        if(topsort()) printf("Yes\n");        else printf("No\n");    }    return 0;}