T103440 【模板】缩点

题目地址

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易错点：

• 出栈时应将inStck[y]置空.

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#include<cstdio>
#include<iostream>
using namespace std;
const int MAXN=1e5,MAXM=1e6;
struct Edge{
	int from,to,nxt;
}e[MAXM];
int head[MAXN],edgeCnt=1;
void addEdge(int u,int v){
	e[++edgeCnt].from=u;
	e[edgeCnt].to=v;
	e[edgeCnt].nxt=head[u];
	head[u]=edgeCnt;
}
int dfn[MAXN],low[MAXN],dfnCnt=0;
int stck[MAXN],top=0;
bool inStck[MAXN];
int inScc[MAXN],sccCnt=0;
int pointVal[MAXN];
int sumVal[MAXN];
void tarjan(int x){
	dfn[x]=low[x]=++dfnCnt;
	stck[++top]=x;
	inStck[x]=1;
	for(int i=head[x];i;i=e[i].nxt){
		int nowV=e[i].to;
		if(!dfn[nowV]){
			tarjan(nowV);
			low[x]=min(low[x],low[nowV]);
		}else if(inStck[nowV]){
			low[x]=min(low[x],dfn[nowV]);
		}
	}
	if(low[x]==dfn[x]){
		int y;
		sccCnt++;
		do{
			y=stck[top--];
			inScc[y]=sccCnt;
			inStck[y]=0;
			sumVal[sccCnt]+=pointVal[y];
		}while(x!=y);
	}
}
bool vis[MAXN];
int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)
		scanf("%d",&pointVal[i]);
	for(int i=1;i<=m;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		addEdge(u,v);
	}
	for(int i=1;i<=n;i++)
		if(!dfn[i])
			tarjan(i);
	for(int i=1;i<=n;i++){
		if(!vis[inScc[i]]){
			vis[inScc[i]]=1;
			printf("%d
",sumVal[inScc[i]]);
		}
	}
	return 0;
}