https://pintia.cn/problem-sets/994805342720868352/problems/994805349394006016
PAT甲级中算是很传统的题了，就是建树，然后遍历即可。
#include<bits/stdc++.h>
using namespace std;
const int N=1e2+10;
int a[N],b[N],n;
unordered_map<int,int>l,r,hush;
int build(int l1,int r1,int l2,int r2)
{
int root=b[r1];
int k=hush[root];
if(k<r2) r[root]=build(r1+k-r2,r1-1,k+1,r2);
if(k>l2) l[root]=build(l1,r1+k-r2-1,l2,k-1);
return root;
}
void solve()
{
vector<int>ve[N];
int deep=0;
queue<pair<int,int>>q; q.push({
b[n],1});
while(q.size())
{
auto t=q.front(); q.pop();
int u=t.first,len=t.second;
ve[len].push_back(u);
if(l[u]) q.push({
l[u],len+1});
if(r[u]) q.push({
r[u],len+1});
deep=max(deep,len);
}
int cnt=0;
for(int i=1;i<=deep;i++)
{
if(i&1) reverse(ve[i].begin(),ve[i].end());
for(int j=0;j<ve[i].size();j++)
{
cnt++;
cout<<ve[i][j];
if(cnt!=n) cout<<" ";
}
}
}
int main(void)
{
cin>>n;
for(int i=1;i<=n;i++) cin>>a[i],hush[a[i]]=i;
for(int i=1;i<=n;i++) cin>>b[i];
build(1,n,1,n);
solve();
return 0;
}