求树的每个子树的重心

#include <iostream>
#include <algorithm>
#include <string>
#include <string.h>
#include <vector>
#include <map>
#include <stack>
#include <set>
#include <queue>
#include <math.h>
#include <cstdio>
#include <iomanip>
#include <time.h>
#include <bitset>
#include <cmath>

#define LL long long
#define INF 0x3f3f3f3f
#define ls nod<<1
#define rs (nod<<1)+1

const double eps = 1e-10;
const int maxn = 3e5 + 10;
const LL mod = 1e9 + 7;

int sgn(double a){return a < -eps ? -1 : a < eps ? 0 : 1;}
using namespace std;

struct edge {
    int v,nxt;
}e[maxn];

int head[maxn],mx[maxn],ans[maxn];
int siz[maxn],fa[maxn];
int cnt;

void add_edge(int u,int v) {
    e[++cnt].v = v;
    e[cnt].nxt = head[u];
    head[u] = cnt;
}

void dfs(int x) {
    siz[x] = 1;
    ans[x] = x;
    int w = 0;
    for (int i = head[x];~i;i = e[i].nxt) {
        int v = e[i].v;
        dfs(v);
        siz[x] += siz[v];
        if (siz[v] > w) {
            w = siz[v];
            mx[x] = v;
        }
    }
    int p = ans[mx[x]];
    while (p && p != fa[x]) {
        if (siz[mx[p]]*2 <= siz[x] && (siz[x]-siz[p])*2 <= siz[x]) {
            ans[x] = p;
            break;
        }
        p = fa[p];
    }
}

int main() {
    cnt = 0;
    memset(head,-1, sizeof(head));
    int n,q;
    scanf("%d%d",&n,&q);
    for (int i = 2;i <= n;i++) {
        int v;
        scanf("%d",&v);
        fa[i] = v;
        add_edge(v,i);
    }
    dfs(1);
    while (q--) {
        int x;
        scanf("%d",&x);
        printf("%d\n",ans[x]);
    }
    return 0;
}