1138 Postorder Traversal（先序+中序=二叉树）

Posted 2021-03-05 keep23456

 大致题意就是给出一个二叉树的先序、中序遍历序列，要求输出二叉树后序遍历的第一个元素。

 1 #include<iostream>
 2 using namespace std;
 3 
 4 const int maxn =  50010;
 5 int n,pre[maxn],in[maxn],flag = 1;
 6 
 7 void create(int preL,int preR,int inL,int inR) {
 8     if(inL > inR ||!flag) return;
 9     int k,leftNum;
10     for(k = inL; k<= inR; ++k)
11         if(in[k] == pre[preL]) break;
12     leftNum = k-inL;
13     create(preL+1,preL+leftNum,inL,k-1);
14     create(preL+leftNum+1,preR,k+1,inR);
15     if(flag) printf("%d",pre[preL]),flag = 0;
16 }
17 
18 int main() {
19     cin>>n;
20     for(int i = 0; i < n; ++i)
21         scanf("%d",&pre[i]);
22     for(int i = 0; i < n; ++i)
23         scanf("%d",&in[i]);
24     create(0,n-1,0,n-1);
25     return 0;
26 }