POJ-1330 Nearest Common Ancestors(lca模板题)

题意：

给定树形图，给定两点，求两点的最近公共祖先。

模板（理论：图论--最近公共祖先LCA-优快云博客）：

#include <algorithm>
#include <string.h>
#include <vector>
#include <cstdio>
#include <cmath> 
using namespace std;
const int maxn = 1e4+5;
int t, n, u, v;
vector<int> g[maxn];
int E[2*maxn], cnt;
int R[maxn], dep[maxn];
int f[2*maxn][20];
int vis[maxn];
void dfs(int u, int fa, int depth)
{
	E[++cnt] = u;
	R[u] = cnt, dep[u] = depth;
	for(int i = 0; i < g[u].size(); ++i)
	{
		int v = g[u][i];
		if(v == fa) continue;
		dfs(v, u, depth+1);
		E[++cnt] = u;
	}
}
void rmq_init(int n)
{
	for(int i = 1; i <= n; ++i) f[i][0] = E[i];
	for(int j = 1; (1<<j) <= n; ++j)
	for(int i = 1; i+(1<<j)-1 <= n; ++i)
	{
		int a = f[i][j-1], b = f[i+(1<<(j-1))][j-1];
		f[i][j] = dep[a] < dep[b]? a: b;
	}
}
int rmq(int l, int r)
{
	int k = log2(r-l+1);
	int a = f[l][k], b = f[r-(1<<k)+1][k];
	return dep[a] < dep[b]? a: b;
}
int lca(int u, int v)
{
	int l = R[u], r = R[v];
	if(l > r) swap(l, r);
	return rmq(l, r);
}
void init()
{
	for(int i = 1; i <= n; ++i) g[i].clear();
	cnt = 0;
	memset(vis, 0, sizeof vis);
}
int main()
{
	for(scanf("%d", &t); t--;)
	{
		scanf("%d", &n); init();
		for(int i = 1; i < n; ++i)
		{
			scanf("%d %d", &u, &v);
			g[u].push_back(v);
			vis[v] = 1;
		}
		scanf("%d %d", &u, &v);
		for(int i = 1; i <= n; ++i)
		if(!vis[i])
		{
			dfs(i, i, 1);
			break;
		}
		rmq_init(cnt);
		printf("%d\n", lca(u, v));
	}
	return 0;
}

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