题干：

给定一棵二叉树的后序遍历和中序遍历，请你输出其层序遍历的序列。这里假设键值都是互不相等的正整数。

解题报告：

   dfs求出这棵树来，然后bfs求层序遍历就行了。

AC代码：

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
#include<map>
#include<vector>
#include<set>
#include<string>
#include<cmath>
#include<cstring>
#define ll long long
#define pb push_back
#define pm make_pair
using namespace std;
const int MAX = 2e5 + 5;
struct Node {int val,l,r;
} node[MAX];
int tot;
int c[MAX],b[MAX]; 
int dfs(int len,int b[],int c[]) {//中序，后序 if(len <= 0) return -1;if(len == 1) {node[++tot].val = b[1];node[tot].l=node[tot].r = -1;return tot;}node[++tot].val = c[len];int res = tot;int l;for(l = 1; l<=len; l++) {if(b[l] == c[len]) break;}node[res].l = dfs(l-1,b,c);//node[res].r = dfs(len-l,b+l-1,c+l);node[res].r = dfs(len-l,b+l,c+l-1);return res;
} 
void bfs() {queue<int> q;q.push(1);while(q.size()) {int cur = q.front();q.pop();if(cur != 1) printf(" ");printf("%d",node[cur].val);if(node[cur].l != -1) q.push(node[cur].l);if(node[cur].r != -1) q.push(node[cur].r);}
}
int main()
{int n;cin>>n;for(int i = 1; i<=n; i++) scanf("%d",c+i);for(int i = 1; i<=n; i++) scanf("%d",b+i);dfs(n,b,c);//printf("%d",node[1].val);bfs();return 0 ;
}