在求LCA的方法上我选取了重链剖分，但是不知为何答案不对

求调

#include<bits/stdc++.h>
using namespace std;
const int N = 5e5 + 5;
int n,m,s,vistime;
int wc[N],sz[N],dep[N],top[N],fa[N];
vector<int> g[N];
void dfs1(int u,int f){
    fa[u] = f;
    dep[u] = dep[f] + 1;
    sz[u] = 1;
    for(auto v : g[u]){
        if(v == f) continue;
        dfs1(v,u);
        sz[u] += sz[v];
        if(sz[v] > sz[wc[u]]) wc[u] = v;
    }
    return;
}
void dfs2(int u,int Top){
    top[u] = Top;
    if(wc[u] != 0){
        dfs2(wc[u],Top);
        for(auto v : g[u]){
            if(v != fa[u] && v != wc[u])
            dfs2(v,v);
        }
    }
}
int qry(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 main(){
    ios:: sync_with_stdio(false);
    cin >> n >> m >> s;
    for(int i = 1; i < n; i ++){
        int u,v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    dfs1(s,0);
    dfs2(s,0);
    while(m --){
        int x,y;
        cin >> x >> y;
        cout << qry(x,y) << endl;
    }
    return 0;
}