LUOGU P3387 【模板】缩点 (缩点+DAG dp)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<queue>

using namespace std;
const int MAXN = 10005;
const int MAXM = 100005;

inline int rd(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)) {f=ch==‘-‘?0:1;ch=getchar();}
    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-‘0‘;ch=getchar();}
    return f?x:-x;
}

int n,m,head[MAXN],cnt,to[MAXM],nxt[MAXM],w[MAXN],wt[MAXN],ans;
int head_[MAXN],cnt_,to_[MAXM],nxt_[MAXM],du[MAXN],f[MAXN];
int dfn[MAXN],low[MAXN],num,stk[MAXN],top,col_num,col[MAXN];
bool vis[MAXN];
queue<int> Q;

inline void add(int bg,int ed){
    to[++cnt]=ed,nxt[cnt]=head[bg],head[bg]=cnt;
}
void tarjan(int x){
    dfn[x]=low[x]=++num;
    stk[++top]=x;vis[x]=1;
    for(register int i=head[x];i;i=nxt[i]){
        int u=to[i];
        if(!dfn[u]) tarjan(u),low[x]=min(low[x],low[u]);
        else if(vis[u]) low[x]=min(dfn[u],low[x]); 
    }
    if(low[x]!=dfn[x]) return;col_num++;
    while(stk[top]!=x) {
        wt[col_num]+=w[stk[top]];
        vis[stk[top]]=0;
        col[stk[top--]]=col_num;
    }top--;
    vis[x]=0;col[x]=col_num;wt[col_num]+=w[x];
}

inline void add_(int bg,int ed){
    to_[++cnt_]=ed,nxt_[cnt_]=head_[bg],head_[bg]=cnt_;
}

int main(){
    n=rd(),m=rd();int x,y,u;
    for(int i=1;i<=n;i++) w[i]=rd();
    for(int i=1;i<=m;i++){
        x=rd(),y=rd();
        add(x,y);
    }
    for(int i=1;i<=n;i++) if(!dfn[i]) tarjan(i);
    for(int i=1;i<=n;i++)
        for(int j=head[i];j;j=nxt[j]){
            u=to[j];
            if(col[u]!=col[i]) add_(col[i],col[u]),du[col[u]]++;
        }
    for(int i=1;i<=col_num;i++) if(!du[i]) Q.push(i),f[i]=wt[i];
    while(!Q.empty()){
        int x=Q.front();Q.pop();
        for(int i=head_[x];i;i=nxt_[i]){
            int u=to_[i];
            f[u]=max(f[u],f[x]+wt[u]);
            du[u]--;if(!du[u]) Q.push(u);
        }
    }
    for(int i=1;i<=col_num;i++) ans=max(ans,f[i]);
    printf("%d",ans);
    return 0;
}