hdu 1269 迷宫城堡（trajan判环）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1269

题意：略

 

题解：trajan模版直接求强连通分量。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
const int N = 1e4 + 10;
const int M = 1e5 + 10;
struct Edge {int v , next;
}edge[M];
int head[N] , e;
int Low[N] , DFN[N] , Stack[N] , Belong[N];
int Index , top;
int scc;
bool Instack[N];
int num[N];
void init() {e = 0;memset(head , -1 , sizeof(head));
}
void add(int u , int v) {edge[e].v = v , edge[e].next = head[u] , head[u] = e++;
}
void Tarjan(int u) {int v;Low[u] = DFN[u] = ++Index;Stack[top++] = u;Instack[u] = true;for(int i = head[u] ; i != -1 ; i = edge[i].next) {v = edge[i].v;if(!DFN[v]) {Tarjan(v);Low[u] = min(Low[u] , Low[v]);}else if(Instack[v]) Low[u] = min(Low[u] , DFN[v]);}if(Low[u] == DFN[u]) {scc++;do {v = Stack[--top];Instack[v] = false;Belong[v] = scc;num[scc]++;}while(v != u);}
}
int main() {int a , b , n , m;while(scanf("%d%d" , &n , &m) != EOF) {if(n == 0 && m == 0) break;init();for(int i = 0 ; i < m ; i++) {scanf("%d%d" , &a , &b);add(a , b);}memset(DFN , 0 , sizeof(DFN));memset(Instack , false , sizeof(Instack));memset(num , 0 , sizeof(num));Index = scc = top = 0;for(int i = 1 ; i <= n ; i++)if(!DFN[i]) Tarjan(i);if(scc == 1) printf("Yes\n");else printf("No\n");}return 0;
}