[AHOI2008]MEET 紧急集合

[AHOI2008]MEET 紧急集合

模板题，容易得到集合点一定在之间。

所以我们只要求出三者的然后求一个总距离最小值去更新答案即可。

树链剖分求也算是倍增吧！

/*
  Author : lifehappy
*/
#include <bits/stdc++.h>

using namespace std;

const int N = 1e6 + 10;

int head[N], to[N], nex[N], cnt = 1;

int fa[N], top[N], son[N], sz[N], dep[N];

int n, m;

void add(int x, int y) {
    to[cnt] = y;
    nex[cnt] = head[x];
    head[x] = cnt++;
}

void dfs1(int rt, int f) {
    fa[rt] = f, dep[rt] = dep[f] + 1;
    sz[rt] = 1;
    for(int i = head[rt]; i; i = nex[i]) {
        if(to[i] == f) continue;
        dfs1(to[i], rt);
        sz[rt] += sz[to[i]];
        if(!son[rt] || sz[son[rt]] < sz[to[i]]) son[rt] = to[i];
    }
}

void dfs2(int rt, int tp) {
    top[rt] = tp;
    if(!son[rt]) return ;
    dfs2(son[rt], tp);
    for(int i = head[rt]; i; i = nex[i]) {
        if(to[i] == fa[rt] || to[i] == son[rt]) continue;
        dfs2(to[i], to[i]);
    }
}

int lca(int x, int y) {
    while(top[x] != top[y]) {
        if(dep[top[x]] < dep[top[y]]) swap(x, y);
        x = fa[top[x]];
    }
    return dep[x] < dep[y] ? x : y;
}

int dis(int x, int y) {
    return dep[x] + dep[y] - 2 * dep[lca(x, y)];
}

int main() {
    // freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
    // ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    scanf("%d %d", &n, &m);
    for(int i = 1; i < n; i++) {
        int x, y;
        scanf("%d %d", &x, &y);
        add(x, y);
        add(y, x);
    }
    dfs1(1, 0);
    dfs2(1, 1);
    for(int i = 1; i <= m; i++) {
        int x, y, z, a[3];
        scanf("%d %d %d", &x, &y, &z);
        a[0] = lca(x, y), a[1] = lca(x, z), a[2] = lca(y, z);
        int ans, res = 0x3f3f3f3f;
        for(int j = 0; j < 3; j++) {
            int temp = dis(a[j], x) + dis(a[j], y) + dis(a[j], z);
            if(temp < res) {
                res = temp;
                ans = a[j];
            }
        }
        printf("%d %d\n", ans, res);
    }
    return 0;
}