LCA模板——倍增法

POJ1330

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <vector>
using namespace std;

typedef long long LL;
const int MOD =  + ;
const int INF = ;
const int N =  + ;
const int LOG = ;

vector<int> G[N];
int parent[LOG][N];
int depth[N];

void dfs(int v, int p, int d) {
    parent[][v] = p;
    depth[v] = d;
    for (int i = ; i < G[v].size(); i++)
        if (G[v][i] != p) dfs(G[v][i], v, d + );
}
void init(int root, int V) {
    dfs(root, -, );
    for (int k = ; k +  < LOG; k++) {
        for (int v = ; v < V; v++) {
            if (parent[k][v] < ) parent[k + ][v] = -;
            else parent[k + ][v] = parent[k][parent[k][v]];
        }
    }
}
int lca(int u, int v) {
    if (depth[u] > depth[v]) swap(u, v);
    for (int k = ; k < LOG; k++) {
        if ((depth[v] - depth[u]) >> k & )
            v = parent[k][v];
    }
    if (u == v) return u;
    for (int k = LOG - ; k >= ; k--) {
        if (parent[k][u] != parent[k][v]) {
            u = parent[k][u];
            v = parent[k][v];
        }
    }
    return parent[][u];
}

bool isroot[N];

int main() {
#ifdef TYH
    freopen("in.txt", "r", stdin);
#endif // TYH
    int T, n;
    scanf("%d", &T);
    while(T--) {
        scanf("%d", &n);
        int a, b;
        for(int i = ; i < n; i++) {
            G[i].clear();
            isroot[i] = true;
        }
        for(int i = ; i < n - ; i++) {
            scanf("%d%d", &a, &b);
            a--, b--;
            G[a].push_back(b);
            G[b].push_back(a);
            isroot[b] = false;
        }
        int root = ;
        for(int i = ;i<n;i++){
            if(isroot[i] == true) root = i;
        }
        init(root, n);
        scanf("%d%d", &a, &b);
        a--, b--;
        printf("%d\n", lca(a, b) + );
    }

    return ;
}