HDU1269

迷宫城堡

题目链接

分类：Graph

1.题目描述

• 给你一个图，要你判断图是否为强连通图。

2.解题思路

• 根据Tarjan算法，直接去强连通缩点，最后判断点是否为1就好了。

3.AC代码

#include <bits/stdc++.h>using namespace std;#define rep(i,a,n) for (int i=a;i<n;i++)#define per(i,a,n) for (int i=n-1;i>=a;i--)#define maxn 10010/* head */struct Edge {    int to, next;} E[maxn << 1];int head[maxn], cnt;int dfn[maxn], low[maxn], s[maxn], belong[maxn], sec, top, scnt;bool inS[maxn];void init() {    memset(head, -1, sizeof head);    memset(dfn, 0, sizeof dfn);    memset(low, 0, sizeof low);    cnt = scnt = sec = top = 0;}void addedge(int u, int v) {    E[cnt].to = v;    E[cnt].next = head[u];    head[u] = cnt++;}void tarjan(int u) {    dfn[u] = low[u] = ++sec;    inS[u] = 1;    s[top++] = 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 (inS[v] && low[u] > dfn[v]) low[u] = dfn[v];    }    if (dfn[u] == low[u]) {        ++scnt;        int tmp;        do {            tmp = s[--top];            inS[tmp] = 0;            belong[tmp] = scnt;        } while (tmp != u);    }}int main() {#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);    long _begin_time = clock();#endif    int n, m;    while (~scanf("%d%d", &n, &m) && m + n) {        init();        while (m--) {            int u, v;            scanf("%d%d", &u, &v);            addedge(u, v);        }        rep(i, 1, n + 1) {            if (!dfn[i]) tarjan(i);        }        puts(scnt == 1 ? "Yes" : "No");    }    return 0;}