【模板】Tarjan scc缩点

代码如下

#include <bits/stdc++.h>
using namespace std;
const int maxv=1e4+10;
const int maxe=1e5+10;

inline int read(){
    int x=0,f=1;char ch;
    do{ch=getchar();if(ch=='-')f=-1;}while(!isdigit(ch));
    do{x=x*10+ch-'0';ch=getchar();}while(isdigit(ch));
    return f*x;
}

struct node{
    int nxt,to;
}e[maxe<<1];
int tot=1,head[maxv];
inline void add_edge(int from,int to){
    e[++tot]=node{head[from],to},head[from]=tot;
}

int n,m,val[maxv],rval[maxv];
int dfs_clk,low[maxv],dfn[maxv],stk[maxv],in[maxv],top;
int scc,cor[maxv];
vector<int> G[maxv];
int dp[maxv],vis[maxv],indeg[maxv],ans;

void tarjan(int u){
    low[u]=dfn[u]=++dfs_clk;
    stk[++top]=u,in[u]=1;
    for(int i=head[u];i;i=e[i].nxt){
        int v=e[i].to;
        if(!dfn[v])tarjan(v),low[u]=min(low[u],low[v]);
        else if(in[v])low[u]=min(low[u],dfn[v]);
    }
    if(dfn[u]==low[u]){
        ++scc;int v;
        do{
            v=stk[top--],in[v]=0;
            cor[v]=scc,rval[scc]+=val[v];
        }while(u!=v);
    }
}

void topo(){
    queue<int> q;
    for(int i=1;i<=scc;i++)if(!indeg[i])q.push(i);
    while(q.size()){
        int u=q.front();q.pop();
        dp[u]+=rval[u],ans=max(ans,dp[u]);
        for(int i=0;i<G[u].size();i++){
            int v=G[u][i];
            dp[v]=max(dp[v],dp[u]);
            if(!--indeg[v])q.push(v);
        }
    }
}

void read_and_parse(){
    n=read(),m=read();
    for(int i=1;i<=n;i++)val[i]=read();
    for(int i=1,x,y;i<=m;i++)x=read(),y=read(),add_edge(x,y);
}

void solve(){
    for(int i=1;i<=n;i++)if(!dfn[i])tarjan(i);
    for(int u=1;u<=n;u++)
        for(int i=head[u];i;i=e[i].nxt){
            int v=e[i].to;
            if(cor[u]==cor[v])continue;
            G[cor[u]].push_back(cor[v]),++indeg[cor[v]];
        }
    topo();
    printf("%d\n",ans);
}

int main(){
    read_and_parse();
    solve();
    return 0;   
}