POJ 2255 二叉树遍历 已知前序遍历 中序遍历 求后序遍历

Description

Little Valentine liked playing with binary trees very much. Her favorite game was constructing randomly looking binary trees with capital letters in the nodes.
This is an example of one of her creations:

 D                                               / \                                             /   \ B     E                                            / \     \                                          /   \     \ A     C     G                                                     /                                                   / F 

To record her trees for future generations, she wrote down two strings for each tree: a preorder traversal (root, left subtree, right subtree) and an inorder traversal (left subtree, root, right subtree). For the tree drawn above the preorder traversal is DBACEGF and the inorder traversal is ABCDEFG.
She thought that such a pair of strings would give enough information to reconstruct the tree later (but she never tried it).

Now, years later, looking again at the strings, she realized that reconstructing the trees was indeed possible, but only because she never had used the same letter twice in the same tree.
However, doing the reconstruction by hand, soon turned out to be tedious.
So now she asks you to write a program that does the job for her!

Input

The input will contain one or more test cases.
Each test case consists of one line containing two strings preord and inord, representing the preorder traversal and inorder traversal of a binary tree. Both strings consist of unique capital letters. (Thus they are not longer than 26 characters.)
Input is terminated by end of file.

Output

For each test case, recover Valentine's binary tree and print one line containing the tree's postorder traversal (left subtree, right subtree, root).

Sample Input

DBACEGF ABCDEFGBCAD CBAD

Sample Output

ACBFGEDCDAB

题意就是 给你二叉树的前序遍历 中序遍历 求后序遍历  

这个是二叉树 后序遍历的应用  注意数组的区间变化 从根节点一点点向下递推 然后再一点点的输出节点

代码如下

#include <stdio.h>#include <iostream>#include <string.h>using namespace std ;char preorder[30] = {'\0'} , inorder[30] = {'\0'};int len ;//函数中的参数为前序和中序遍历所对应的数组区间下标void build(int prel , int prer ,int inl , int inr){if(prel > prer) return ;char temp = preorder[prel] ;int num ;//在中序遍历结果中找前序遍历的节点位置，以此来划分递归区间for(int i = inl ; i <= inr ; i ++){if(inorder[i] == temp){num = i - inl ;break ;}}build(prel + 1 , prel + num , inl , inl + num-1) ;//左子树build(prel + 1 + num , prer , inl + num + 1 , inr) ;//右子树cout << temp ;}int main(){while(cin >> preorder >> inorder){len = strlen(preorder) ;build(0 , len - 1 , 0 , len - 1) ;cout << endl ;}return 0;}

顺便感慨一下 C++比C好写的多