LuoguP3387 tarjan缩点+拓扑图dp

如题

#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
#include<vector>
#include<cstdio> 
using namespace std;

const int Maxn = 1e4+10,Maxm = 1e5+10; 

struct Edge{
    int to,ne;
}edges[Maxm];

vector<int> scc[Maxn],g[Maxn];
int first[Maxn],dfn[Maxn],low[Maxn],stack[Maxn],ins[Maxn],inscc[Maxn];
int val[Maxn],sval[Maxn],ind[Maxn],f[Maxn];
int n,m,cnte,cntv,cntscc,top;

int read(){
    int a = 0;char l = ' ',c = getchar();
    while(c < '0'||c > '9')l = c,c = getchar();
    while('0' <= c&&c <= '9')a = a*10+c-'0',c = getchar();
    if(l == '-')return -a;return a;
}

void add_edge(int fr,int to){
    edges[++cnte] = (Edge){to,first[fr]};
    first[fr] = cnte;
}

void dfs(int x){//printf("dfs::%d  ",x);
    low[x] = dfn[x] = ++cntv;
    ins[x] = 1,stack[++top] = x;
    for(int i = first[x];i;i = edges[i].ne){
        Edge e = edges[i];
        if(!dfn[e.to])dfs(e.to),low[x] = min(low[x],low[e.to]);
        else if(ins[e.to])low[x] = min(low[x],dfn[e.to]);
    }
    if(dfn[x] == low[x]){
        int y = 0;
        cntscc++;
        while(y != x){
            y = stack[top--];
            ins[y] = 0,inscc[y] = cntscc;
            scc[cntscc].push_back(y);
        }
    }
}

int ans = 0;
void toposort(){
    queue<int> q;
    for(int i = 1;i <= cntscc;i++)if(!ind[i])q.push(i);
    while(!q.empty()){
        int u = q.front();q.pop();
        f[u] += sval[u];//printf("%d ",u);
        ans = max(ans,f[u]);
        for(int i = 0;i < g[u].size();i++){
            int v = g[u][i];
            ind[v]--;
            f[v] = max(f[v],f[u]);
            if(!ind[v])q.push(v);
        }
    }
}

int main(){
    cin >> n >> m;
    for(int i = 1;i <= n;i++)val[i] = read();
    for(int i = 1;i <= m;i++)add_edge(read(),read());
    for(int i = 1;i <= n;i++)if(!dfn[i])dfs(i);//putchar('
');
    for(int i = 1;i <= cntscc;i++){
        for(int j = 0;j < scc[i].size();j++){
            int u = scc[i][j];
            sval[i] += val[u];
            for(int k = first[u];k;k = edges[k].ne){
                Edge e = edges[k];
                if(inscc[e.to] == i)continue;
                g[i].push_back(inscc[e.to]);
                ind[inscc[e.to]]++;
            }
        }
    }
    
//    for(int i = 1;i <= n;i++)printf("%d:%d ",i,inscc[i]);putchar('
');
//    for(int i = 1;i <= cntscc;i++)printf("%d:%d ",i,sval[i]);putchar('
');
    
    toposort();
    cout << ans;
return 0;
}