[HDOJ1269]迷宫城堡（有向图强连通分量）

#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <climits>
#include <complex>
#include <fstream>
#include <cassert>
#include <cstdio>
#include <bitset>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <ctime>
#include <set>
#include <map>
#include <cmath>

using namespace std;

const int maxn = 11111;
const int maxm = 100010;
typedef struct Edge {
int v;
int next;
Edge() { next = -1; }
}Edge;

int head[maxn], ecnt;
Edge edge[maxm];
int n, m;

int bcnt, idx;
int dfn[maxn], low[maxn];
int stk[maxn], top;
int group[maxn];
bool instk[maxn];

void init() {
memset(edge, 0, sizeof(edge));
memset(head, -1, sizeof(head));
memset(instk, 0, sizeof(instk));
memset(dfn, 0, sizeof(dfn));
memset(low, 0, sizeof(low));
memset(group, 0, sizeof(group));
ecnt = top = bcnt = idx = 0;
}

void adde(int uu, int vv) {
edge[ecnt].v = vv;
edge[ecnt].next = head[uu];
head[uu] = ecnt++;
}

void tarjan(int u) {
int v = u;
dfn[u] = low[u] = ++idx;
stk[++top] = u;
instk[u] = 1;
for(int i = head[u]; ~i; i=edge[i].next) {
v = edge[i].v;
if(!dfn[v]) {
tarjan(v);
low[u] = min(low[u], low[v]);
}
else if(instk[v] && dfn[v] < low[u]) {
low[u] = dfn[v];
}
}
if(dfn[u] == low[u]) {
bcnt++;
do {
v = stk[top--];
instk[v] = 0;
group[v] = bcnt;
}while(v != u);
}
}

int main() {
// freopen("in", "r", stdin);
int uu, vv;
while(~scanf("%d %d", &n, &m) && n + m) {
init();
for(int i = 0; i < m; i++) {
scanf("%d %d", &uu, &vv);
adde(uu, vv);
}
for(int i = 1; i <= n; i++) {
if(!dfn[i]) {
tarjan(i);
}
}
if(bcnt > 1) {
printf("No\n");
}
else {
printf("Yes\n");
}
}
return 0;
}