倍增lca样例过了0分求调

#include <bits/stdc++.h>
using namespace std;

int tree[500005][30];//i点2^j祖先
int  deep[500005];
int n,m,s;
void bd(int cur){
    if (cur==s||deep[cur]) return;
    bd(tree[cur][1]);
    deep[cur]=deep[tree[cur][1]]+1;
}
void build(){
	deep[0]=-114514;
    int a,b;
    for (int i=1;i<n;i++){
        cin>>a>>b;
        tree[a][1]=b;
    }
    for (int i=2;i<=25;i++){
        for (int j=1;j<=n;j++){
            tree[j][i]=tree[tree[j][i-1]][i-1];
        }
    }
    for (int i=1;i<=n;i++) bd(i);
    return;
}
int todeep(int num,int dp){
    if (deep[num]==dp) return num;
    int i=25;
    while (deep[tree[num][i]]<dp) i--;
    return todeep(tree[num][i],dp);
}
int c(int a,int b){
	if (a!=b&&tree[a][1]==tree[b][1]) return tree[b][1];
    int i=25;
    while (tree[a][i]==tree[b][i]&&i>=1) i--;
    return c(tree[a][i],tree[b][i]);
}
int lca(int s,int b){
    b=todeep(b,deep[s]);
    if (s==b) return s;
    return c(s,b);
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
    int a,b;
    cin>>n>>m>>s;
    build();
    while (m--){
        cin>>a>>b;
        if (deep[a]<deep[b]) cout<<lca(a,b)<<"\n";
        else cout<<lca(b,a)<<"\n";
    }
    return 0;
}