HDU1269 - 迷宫城堡 - 图论

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 
using namespace std;
#define rep(i,a,n) for (int i=a;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;
}