tarjan 割点 缩点

割点

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<cmath>
#include<map>
#include<algorithm>
using namespace std;
#define ll long long
#define lb long double
#define INF 0x3f3f3f3f
#define maxn 100005
int n, m, cnt, deep, ans;
int head[maxn], low[maxn], dfn[maxn], flag[maxn];
struct node{
    int to;
    int next;
}edge[maxn << 1];
void add(int u, int v){
    edge[cnt].to = v;
    edge[cnt].next = head[u];
    head[u] = cnt ++;
}
void tarjan(int u, int fa){
    deep ++;
    low[u] = dfn[u] = deep;
    int child = 0;
    for(int i = head[u] ; i != -1 ; i = edge[i].next){
        int v = edge[i].to;
        if(!dfn[v]){
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(low[v] >= dfn[u] && u != fa) flag[u] = 1;
            else if(u == fa) child ++;
        }
        else low[u] = min(low[u], dfn[v]);
    }
    if(u == fa && child >= 2) flag[u] = 1;
}
int main()
{
    int u, v;
    scanf("%d %d", &n, &m);
    for(int i = 1 ; i <= n ; ++ i) head[i] = -1;
    for(int i = 1 ; i <= m ; ++ i){
        scanf("%d %d", &u, &v);
        add(u, v); add(v, u);
    }
    for(int i = 1 ; i <= n ; ++ i){
        if(!dfn[i]) tarjan(i, i);
    }
    for(int i = 1 ; i <= n ; ++ i){
        if(flag[i]) ans ++;
    }
    cout << ans << endl;
    for(int i = 1 ; i <= n ; ++ i){
        if(flag[i]) cout << i << " ";
    }
    return 0;
}

缩点

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<cmath>
#include<stack>
#include<map>
#include<algorithm>
using namespace std;
#define ll long long
#define lb long double
#define INF 0x3f3f3f3f
#define maxn 100010
int n, m, cnt, deep, num, ct, maxi;
int head[maxn], hd[maxn], vis[maxn], dfn[maxn], low[maxn], col[maxn], a[maxn], b[maxn], du[maxn], dp[maxn];
stack<int> s;
struct node{
    int to;
    int next;
}edge[maxn << 1], ed[maxn << 1];
void add(int u, int v){
    edge[cnt].to = v;
    edge[cnt].next = head[u];
    head[u] = cnt ++;
}
void tarjan(int u){
    deep ++;
    dfn[u] = low[u] = deep;
    vis[u] = 1;
    s.push(u);
    for(int i = head[u] ; i != -1 ; i = edge[i].next){
        int v = edge[i].to;
        if(!dfn[v]){
            tarjan(v);
            low[u] = min(low[u], low[v]);
        }
        else{
            if(vis[v]){
                low[u] = min(low[u], dfn[v]);
            }
        }
    }
    if(low[u] == dfn[u]){
        col[u] = ++ num;
        vis[u] = 0;
        while(s.top() != u){
            col[s.top()] = num;
            vis[s.top()] = 0;
            s.pop();
        }
        s.pop();
    }
}
int main()
{
    int u, v;
    scanf("%d %d", &n, &m);
    for(int i = 1 ; i <= n ; ++ i) head[i] = -1;
    for(int i = 1 ; i <= n ; ++ i) hd[i] = -1;
    for(int i = 1 ; i <= n; ++ i){
        scanf("%d", &a[i]);
    }
    for(int i = 1 ; i <= m ; ++ i){
        scanf("%d %d", &u, &v);
        add(u, v);
    }
    for(int i = 1 ; i <= n ; ++ i){
        if(!dfn[i]){
            tarjan(i);
        }
    }
    for(int i = 1 ; i <= n ; ++ i){
        b[col[i]] += a[i];
    }
    for(int i = 1 ; i <= n ; ++ i){
        for(int j = head[i] ; j != -1 ; j = edge[j].next){
            int uu = col[i], vv = col[edge[j].to];
            if(uu != vv){
                ed[ct].to = vv; ed[ct].next = hd[uu]; hd[uu] = ct ++;
                du[vv] ++;
            }
        }
    }
    queue<int> que;
    for(int i = 1 ; i <= num ; ++ i){
        dp[i] = b[i];
        maxi = max(maxi, dp[i]);
        /*if(hd[i] != -1)
        cout << ed[hd[i]].to << endl;*/
        if(du[i] == 0){
            que.push(i);
            du[i] = -1;
        }
    }
    while(!que.empty()){
        int cur = que.front();
        que.pop();
        for(int i = hd[cur] ; i != -1 ; i = ed[i].next){
            int tt = ed[i].to;
            du[tt] --;
            if(du[tt] == 0){
                dp[tt] = max(dp[tt], dp[cur] + b[tt]);
                maxi = max(maxi, dp[tt]);
                que.push(tt);
                du[tt] = -1;
            }
        }
    }
    cout << maxi;
    return 0;
}