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：

#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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