post是后序遍历数组，mid是中序遍历数组
l1,r1是中序遍历区间,l2,r2是后序遍历区间

#include<iostream>
#include<queue>
using namespace std;
int n,post[35],mid[35];
int ans[35],m;
struct Node{
    int l,r;
}tr[35];
int build(int l1,int r1,int l2,int r2){
    if(l1>r1) return 0;
    int rt=post[r2];
    int i=l1;
    while(mid[i]!=rt) i++;
    int cnt=i-l1;
    tr[rt].l=build(l1,i-1,l2,l2+cnt-1);
    tr[rt].r=build(i+1,r1,l2+cnt,r2-1);
    return rt;
}
void bfs(int rt){
    queue<int> q;
    q.push(rt);
    while(!q.empty()){
        int t=q.front();q.pop();
        ans[++m]=t;
        int l=tr[t].l,r=tr[t].r;
        if(l!=0) q.push(l);
        if(r!=0) q.push(r);
    }
}
int main(){
    cin >> n;
    for(int i=1;i<=n;i++) cin >> post[i];
    for(int i=1;i<=n;i++) cin >> mid[i];
    int rt=build(1,n,1,n);
    bfs(rt);
    for(int i=1;i<=m;i++){
        cout << ans[i];
        if(i!=m) cout << ' ';
    }
    return 0;
}