【强连通分量】 HDOJ 1269 迷宫城堡

#include <iostream>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 10005
#define maxm 100005
#define eps 1e-10
#define mod 1000000009
#define INF 99999999
#define lowbit(x) (x&(-x))
//#define lson o<<1, L, mid
//#define rson o<<1 | 1, mid+1, R
typedef long long LL;
//typedef int LL;
using namespace std;

int H[maxn], v[maxm], next[maxm];
int dfn[maxn], low[maxn], in[maxn];
int f[maxn], n, m, top;
stack<int> s;

void scanf(int &x)
{
x = 0;
char ch = getchar();
while(ch == ' ' || ch == '\n') ch = getchar();
while(ch >= '0' && ch <= '9') x = x*10+ch-'0', ch = getchar();
}
void read(void)
{
int cnt = 0, a, b;
while(m--) {
//scanf("%d%d", &a, &b);
scanf(a), scanf(b);
next[cnt] = H[a], H[a] = cnt, v[cnt] = b, cnt++;
}
}
void init(void)
{
top = 0;
memset(f, 0, sizeof f);
memset(in, 0, sizeof in);
memset(H, -1, sizeof H);
memset(dfn, 0, sizeof dfn);
}
void tarjan(int u)
{
low[u] = dfn[u] = ++top;
s.push(u), in[u] = 1;
for(int e = H[u]; ~e; e = next[e]) {
if(!dfn[v[e]]) {
tarjan(v[e]);
low[u] = min(low[v[e]], low[u]);
}
else if(in[v[e]]) low[u] = min(dfn[v[e]], low[u]);
}
if(dfn[u] == low[u]) {
int tmp = s.top();
s.pop();
in[tmp] = 0;
while(tmp != u) {
f[tmp] = u;
tmp = s.top();
s.pop();
in[tmp] = 0;
}
f[tmp] = u;
}
}
void work(void)
{
for(int i = 1; i <= n; i++)
if(!dfn[i]) tarjan(i);
int ok = 1;
for(int i = 2; i <= n; i++)
if(f[i] != f[i-1]) {
ok = 0;
break;
}
if(ok) printf("Yes\n");
else printf("No\n");
}
int main(void)
{
while(scanf(n), scanf(m), n != 0 || m != 0) {
init();
read();
work();
}
return 0;
}