http://acm.hdu.edu.cn/showproblem.php?pid=1710

已知先序和中序遍历，求后序遍历二叉树。

思路：先递归建树的过程，后后序遍历。

Binary Tree Traversals

Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3442    Accepted Submission(s): 1541

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.

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

Source

HDU 2007-Spring Programming Contest

#include<iostream>
#include<cstring>
#include<cstdio>
#include<stdlib.h>
using namespace std;
int m;
typedef struct tree
{
    tree *l,*r;
    int num;
}tree;
tree *creat(int *a,int *b,int n)
{
    tree *t;
    int i;
    for(i=0;i<n;i++)
    {
       if(a[0]==b[i])//找到中序遍历时的根节点
       {
           t=(tree*)malloc(sizeof(tree));
           t->num=b[i];
           t->l=creat(a+1,b,i);//中序历遍中在根节点左边的都是左子树上的
           t->r=creat(a+i+1,b+i+1,n-i-1);//在根节点右边的，都是右子树上的，右子树需要从i+1开始
           return t;
       }
    }
    return NULL;
}
void postorder(tree *root)//后序遍历。
{
    if(root!=NULL)
    {
        postorder(root->l);
        postorder(root->r);
        if(m==root->num)
        printf("%d\n",root->num);
        else
          printf("%d ",root->num);
    }
}

int main()
{
    int i,n;
    int a[2005],b[2005];
    while(~scanf("%d",&n))
    {
        tree *root;
        for(i=0;i<n;i++)
        scanf("%d",&a[i]);
        for(i=0;i<n;i++)
        scanf("%d",&b[i]);
        root=creat(a,b,n);
        m=a[0];
       // printf("root=%d\n",root->num);
         postorder(root);

    }
    return 0;
}