Binary Tree Traversals hdu 1710 c++

水深无声 2022-08-10 13:50 9阅读 0赞

# Binary Tree Traversals #

**Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)  
Total Submission(s): 3320    Accepted Submission(s): 1491**

Problem Description

A binary tree is a finite set of vertices that is either empty or consists of a root r and two disjoint binary trees called the left and right subtrees. There are three most important ways in which the vertices of a binary tree can be systematically traversed or ordered. They are preorder, inorder and postorder. Let T be a binary tree with root r and subtrees T1,T2.  
  
In a preorder traversal of the vertices of T, we visit the root r followed by visiting the vertices of T1 in preorder, then the vertices of T2 in preorder.  
  
In an inorder traversal of the vertices of T, we visit the vertices of T1 in inorder, then the root r, followed by the vertices of T2 in inorder.  
  
In a postorder traversal of the vertices of T, we visit the vertices of T1 in postorder, then the vertices of T2 in postorder and finally we visit r.  
  
Now you are given the preorder sequence and inorder sequence of a certain binary tree. Try to find out its postorder sequence.  
![C57-1005-1.jpg][]

Input

The input contains several test cases. The first line of each test case contains a single integer n (1<=n<=1000), the number of vertices of the binary tree. Followed by two lines, respectively indicating the preorder sequence and inorder sequence. You can assume they are always correspond to a exclusive binary tree.

Output

For each test case print a single line specifying the corresponding postorder sequence.

Sample Input

9
    1 2 4 7 3 5 8 9 6
    4 7 2 1 8 5 9 3 6

Sample Output

7 4 2 8 9 5 6 3 1

题意：给你一个树的先序和中序，输出后序序列；

思路：递归调用，不断的找出根，输出；

#include<stdio.h>
    
    void build_tree(int n,int *a,int *b,int *c)
    {     
        int *p=b,tt=0;
        if(n<=0)
            return;
        while(1)
        {
            if(a[0]==*p)
            {//找到中序表示中根的位置 
                break;
            }
            else p++;
        }
        tt=p-b;//左子树长度； 
        build_tree(tt,a+1,b,c);
        build_tree(n-tt-1,a+tt+1,b+tt+1,c+tt);
        c[n-1]=a[0];
    }
    int main(){  
       int n,i;
       while(~scanf("%d",&n))
            {
            int a[1002],b[1002],c[1002];
            for(i=0;i<n;i++){//先序数组 
                scanf("%d",&a[i]);
            }
            for(i=0;i<n;i++){//中序数组 
                scanf("%d",&b[i]);
            }
            build_tree(n,a,b,c);
        
            for(i=0;i<n-1;i++){
                 printf("%d ",c[i]);
            }
            printf("%d\n",c[n-1]);
       }
       return 0;
    }

[C57-1005-1.jpg]: /images/20220810/46672a5e9a5e43959b0e57182c72a881.png