# BZOJ1051 [HAOI2006]受欢迎的牛(Tarjan缩点)

/**************************************************************
Problem: 1051
Language: C++
Result: Accepted
Time:116 ms
Memory:2724 kb
****************************************************************/

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string>
//#include<stack>
#include<queue>
#include<deque>
#include<set>
#include<vector>
#include<map>
#include<functional>

#define fst first
#define sc second
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,root<<1
#define rson mid+1,r,root<<1|1
#define lc root<<1
#define rc root<<1|1
#define lowbit(x) ((x)&(-x))

using namespace std;

typedef double db;
typedef long double ldb;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> PI;
typedef pair<ll,ll> PLL;

const db eps = 1e-6;
const int mod = 100003;
const int maxn = 2e5+100;
const int maxm = 2e5+100;
const ll inf = 0x3f3f3f3f3f3f3f3f;
const db pi = acos(-1.0);
int color[10010],dfn[20020],low[20020],stack[20020],vis[10010],cnt[10010];
int top,n,m,sum,ans;
int deep = 0;
vector<int>g[10010];
vector<int>rg[10010];
void tarjan(int u){
dfn[u]=++deep;
low[u]=deep;
vis[u]=1;
stack[++top]=u;
int sz=g[u].size();
for(int i=0;i<sz;i++){
int v=g[u][i];
if(!dfn[v]){
tarjan(v);
low[u]=min(low[u],low[v]);
}
else{
if(vis[v]){
low[u]=min(low[u],low[v]);
}
}
}
if(dfn[u]==low[u]){
color[u]=++sum;
vis[u]=0;
while(stack[top]!=u){
color[stack[top]]=sum;
vis[stack[top--]]=0;
}
top--;
}
return;
}
int res = 0;
int num[10010];
void rb(){
for(int i = 1; i <= n; i++){
num[color[i]]++;
int sz = g[i].size();
for(int j = 0; j < sz; j++){
int u = g[i][j];
if(color[i]!=color[u]){
rg[color[i]].pb(color[u]);
}
}
}
int flg = 0;
for(int i = 1; i <= sum; i++){
//printf("%d %d\n", i, rg[i].size());
if(rg[i].size()==0){
if(flg==0)flg = i;
else flg = -1;
}
}

if(flg==-1)flg = 0;
else flg = num[flg];
printf("%d", flg);
}
int main() {
sum = 0;
mem(num, 0);
scanf("%d %d", &n, &m);
for(int i = 1; i <= m; i++){
int from, to;
scanf("%d %d", &from, &to);
g[from].pb(to);
}
for(int i = 1; i <= n; i++){
if(!dfn[i])tarjan(i);
}
//for(int i = 1; i <= n; i++)printf("%d %d\n",i, color[i] );
//printf("%d\n", sum);
rb();
return 0;
}

posted @ 2018-10-03 00:30  wrjlinkkkkkk  阅读(62)  评论(0编辑  收藏