[模板]tarjan算法求SCC

[模板]tarjan算法求SCC

• HDU 1269 迷宫城堡

#include <iostream>
#include <cstdio>
#include <cstring>
#include <stack>

using namespace std;

struct Edge {
    int to, next;
    Edge(int _to = 0, int _next = 0) : to(_to), next(_next) {}
};

const int MAX_N = 1e4 + 7;
const int MAX_M = 1e5 + 7;
Edge e[MAX_M];
int dfn[MAX_N], low[MAX_N], head[MAX_N];
bool vis[MAX_N];
stack <int> st;
int cnt, order, mx;

void add(int a, int b) { e[++cnt].to = b; e[cnt].next = head[a]; head[a] = cnt; }
void tarjan(int u) {
    dfn[u] = low[u] = ++order;
    vis[u] = true;
    st.push(u);
    for(int i = head[u]; i; i = e[i].next) {
        int v = e[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(dfn[u] == low[u]) {
        int num = 0, tmp;
        do {
            tmp = st.top(); 
            st.pop();
            vis[tmp] = false;
            num++;
        }while(tmp != u);
        mx = max(mx, num);
    }
}
int main() {
    while(true) {
        int n, m;
        scanf("%d%d", &n, &m);
        if(n == m && n == 0) break;
        cnt = order = mx = 0;
        for(int i = 1; i <= n; i++) dfn[i] = low[i] = head[i] = 0;
        for(int i = 1; i <= m; i++) {
            int a, b;
            scanf("%d%d", &a, &b);
            add(a, b);
        }
        tarjan(1);
        if(mx == n) {
            puts("Yes");
        } else {
            puts("No");
        }
    }
    return 0;
}