1020. Tree Traversals (25)-PAT甲级真题(后序中序转层序)

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=30), the total number of nodes in the binary tree. The second line gives the postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in one line the level order traversal sequence of the corresponding binary tree. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.

Sample Input:
7
2 3 1 5 7 6 4
1 2 3 4 5 6 7

Sample Output:
4 1 6 3 5 7 2

题目大意: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。

分析:与后序中序转换为前序的代码相仿(无须构造二叉树再进行广度优先搜索~),只不过加一个变量index,表示当前的根结点在二叉树中所对应的下标(从0开始),所以进行一次输出先序的递归过程中,就可以把根结点下标index及所对应的值存储在map<int, int> level中,map是有序的会根据index从小到大自动排序,这样递归完成后level中的值就是层序遍历的顺序~~

如果你不知道如何将后序和中序转换为先序,请看:https://www.liuchuo.net/archives/2090

 

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