POJ 2762 Going from u to v or from v to u?(强连通分量+拓扑排序)

#include <iostream>
#include <string.h>
#include <math.h>
#include <queue>
#include <algorithm>
#include <stdlib.h>
#include <map>
#include <set>
#include <stdio.h>
using namespace std;
#define LL __int64
#define pi acos(-1.0)
const int mod=1e9+7;
const int INF=0x3f3f3f3f;
const double eqs=1e-9;
const int MAXN=1000+10;
int head[MAXN], Ecnt, scc, top, indx;
int low[MAXN], dfn[MAXN], belong[MAXN], stk[MAXN], instack[MAXN];
struct node
{
int u, v, next;
}edge[7000];
void add(int u, int v)
{
edge[Ecnt].v=v;
edge[Ecnt].next=head[u];
head[u]=Ecnt++;
}
void tarjan(int u)
{
low[u]=dfn[u]=++indx;
instack[u]=1;
stk[++top]=u;
for(int i=head[u];i!=-1;i=edge[i].next){
int v=edge[i].v;
if(!dfn[v]){
tarjan(v);
low[u]=min(low[u],low[v]);
}
else if(instack[v]){
low[u]=min(low[u],dfn[v]);
}
}
if(low[u]==dfn[u]){
scc++;
while(1){
int v=stk[top--];
belong[v]=scc;
instack[v]=0;
if(u==v) break;
}
}
}
void init()
{
memset(head,-1,sizeof(head));
memset(dfn,0,sizeof(dfn));
memset(instack,0,sizeof(instack));
Ecnt=top=indx=scc=0;
}
int head1[MAXN], Ecnt1, deg[MAXN];
struct node1
{
int u, v, next;
}edge1[7000];
void add1(int u, int v)
{
edge1[Ecnt1].v=v;
edge1[Ecnt1].next=head1[u];
head1[u]=Ecnt1++;
}
bool topo(int scc)
{
int i, u, tot, m=scc;
while(m--){
tot=0;
for(i=1;i<=scc;i++){
if(!deg[i]){
tot++;
u=i;
deg[i]--;
}
}
if(tot>1) return false;
for(i=head1[u];i!=-1;i=edge1[i].next){
deg[edge1[i].v]--;
}
}
return true;
}
void init1()
{
memset(deg,0,sizeof(deg));
memset(head1,-1,sizeof(head1));
Ecnt1=0;
}
int main()
{
int n, m, i, j, u, v, t, f;
scanf("%d",&t);
while(t--){
scanf("%d%d",&n,&m);
init();
while(m--){
scanf("%d%d",&u,&v);
add(u,v);
}
for(i=1;i<=n;i++){
if(!dfn[i])
tarjan(i);
}
init1();
for(i=1;i<=n;i++){
for(j=head[i];j!=-1;j=edge[j].next){
v=edge[j].v;
if(belong[i]!=belong[v]){
add1(belong[i],belong[v]);
deg[belong[v]]++;
//printf("%d %d\n",belong[i],belong[v]);
}
}
}
if(topo(scc)) puts("Yes");
else puts("No");
}
return 0;
}