PAT (Advanced Level) Practice 1020 Tree Traversals (25 分)

July 22, 2019

320views

2175 words

**1020 Tree Traversals (25 分)**

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
```
后中序遍历构建二叉树并输出层次遍历
```
#include <iostream>
#include <queue>
#define MAXSIZE 31
using namespace std;
int in[MAXSIZE], post[MAXSIZE], n;
struct node
{
 int v;
 node *left, *right;
};
node *create(int inl, int inr, int postl, int postr)
{
 if (postl > postr)
 return NULL;
 node *root = new node;
 root->v = post[postr];
 int i = 0;
 for (i = inl; i <= inr; i++)
 {
 if (in[i] == post[postr])
 break;
 }
 root->left = create(inl, i - 1, postl, postl + i - inl - 1);
 root->right = create(i + 1, inr, postl + i - inl, postr - 1);
 return root;
}
void travel()
{
 queue<node *> q;
 node *root = create(0, n-1, 0, n-1);
 q.push(root);
 bool flag = false;
 while (!q.empty())
 {
 root = q.front();
 q.pop();
 if (flag)
 cout << " ";
 flag = true;
 cout << root->v;
 if(root->left!=NULL)q.push(root->left);
 if(root->right!=NULL)q.push(root->right);
 }
}
int main()
{
 std::ios::sync_with_stdio(false);
 std::cin.tie(0);
 cin >> n;
 for (int i = 0; i < n; i++)
 cin >> post[i];
 for (int i = 0; i < n; i++)
 cin >> in[i];
 travel();
 return 0;
}
```

![PAT (Advanced Level) Practice 1020 Tree Traversals.png][1]

[1]: http://alomerry.com/usr/uploads/2020/01/587723404.png<hr class="content-copyright" style="margin-top:50px" /><blockquote class="content-copyright" style="font-style:normal">版权属于：清欢本文链接：<a class="content-copyright" href="http://alomerry.com/archives/53/">http://alomerry.com/archives/53/</a>转载时须注明出处及本声明</blockquote>

Last modification：July 2nd, 2020 at 10:53 pm

觉得我的文章有帮助吗，欢迎赞赏呀(๑• . •๑)

PAT (Advanced Level) Practice 1020 Tree Traversals (25 分)