Tarjan求LCA

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<queue>
#include<cstring>
#define rep(i,a,n) for(int i = a;i <= n;i++)
#define per(i,n,a) for(int i = n;i >= a;i--)
#define enter putchar(‘\n‘)
#define pr pair<int,int>
#define mp make_pair
#define fi first
#define sc second
using namespace std;
typedef long long ll;
const int M = 500005;
const int N = 10000005;
 
int read()
{
    int ans = 0,op = 1;
    char ch = getchar();
    while(ch < ‘0‘ || ch > ‘9‘)
    {
    if(ch == ‘-‘) op = -1;
    ch = getchar();
    }
    while(ch >=‘0‘ && ch <= ‘9‘)
    {
    ans *= 10;
    ans += ch - ‘0‘;
    ch = getchar();
    }
    return ans * op;
}

struct edge
{
    int next,to,id;
}e[M<<2],q[M<<2];

int n,m,s,x,y,head[M],qhead[M],ecnt,qcnt,fa[M],lca[M];
bool vis[M];

int getfa(int x)
{
    return fa[x] == x ? x : fa[x] = getfa(fa[x]);
}

void add(int x,int y)
{
    e[++ecnt].to = y;
    e[ecnt].next = head[x];
    head[x] = ecnt;
}

void addq(int x,int y,int g)
{
    q[++qcnt].to = y;
    q[qcnt].next = qhead[x];
    q[qcnt].id = g;
    qhead[x] = qcnt;
}

void tarjan(int x,int f)
{
    for(int i = head[x];i;i = e[i].next)
    {
    if(e[i].to == f  || vis[e[i].to]) continue;
    tarjan(e[i].to,x);
    fa[e[i].to] = x;
    }
    for(int i = qhead[x];i;i = q[i].next)
    {
    if(!vis[q[i].to]) continue;
    lca[q[i].id] = getfa(q[i].to);
    }
    vis[x] = 1;
}

int main()
{
    n = read(),m = read(),s = read();
    rep(i,1,n-1) x = read(),y = read(),add(x,y),add(y,x),fa[i] = i;
    fa[n] = n;
    rep(i,1,m) x = read(),y = read(),addq(x,y,i),addq(y,x,i);
    tarjan(s,s);
    rep(i,1,n) printf("%d\n",lca[i]);
    return 0;
}