【LCA】 POJ 1330 Nearest Common Ancestors

LCA模板题。。用一下tarjan的离线算法就行了。。。

#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 40005
#define eps 1e-10
#define mod 1000000007
#define INF 999999999
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
//typedef vector<int>::iterator IT;
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
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();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

int h[maxn], next[maxm], v[maxm];
int f[maxn], in[maxn];
int vis[maxn], ancestor[maxn];
int n, s, t, cnt, ok;

void addedges(int a, int b) 
{
	next[cnt] = h[a], h[a] = cnt, v[cnt] = b, cnt++;
}
int find(int u) 
{
	return u == f[u] ? f[u] : find(f[u]);
}
void merge(int a, int b) 
{
	int aa = find(a), bb = find(b);f[aa] = f[bb];
}
void lca(int u)
{
	ancestor[u] = u;
	for(int e = h[u]; ~e; e = next[e]) {
		lca(v[e]);
		merge(u, v[e]);
		ancestor[find(u)] = u;
	}
	vis[u] = 1;
	if(u == s && vis[t] && ok) ok = 0, printf("%d\n", ancestor[find(t)]);
	if(u == t && vis[s] && ok) ok = 0, printf("%d\n", ancestor[find(s)]);
}
void init(void)
{
	cnt = 0, ok = 1;
	memset(h, -1, sizeof h);
	memset(in, 0, sizeof in);
	memset(vis, 0, sizeof vis);
}
void read(void)
{
	int a, b;
	scanf("%d", &n);
	for(int i = 1; i < n; i++) {
		scanf("%d%d", &a, &b);
		in[b]++;
		addedges(a, b);
	}
	scanf("%d%d", &s, &t);
}
void work(void)
{
	for(int i = 1; i <= n; i++) f[i] = i;
	for(int i = 1; i <= n; i++) if(!in[i]) lca(i);
}
int main(void)
{
	int _;
	while(scanf("%d", &_)!=EOF) {
		while(_--) {
			init();
			read();
			work();
		}
	}
	return 0;
}