PAT 1020. Tree Traversals (25)

1020. Tree Traversals (25)

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


 1 #include <iostream>
 2 #include <queue>
 3 
 4 using namespace std;
 5 
 6 struct Node
 7 {
 8     int val;
 9     Node* left;
10     Node* right;
11     Node(){ val = 0; left = right = nullptr; }
12 };
13 
14 static int postOrder[30];
15 static int inOrder[30];
16 
17 int InOrderFindIndex(int val, int inLeft, int inRight)
18 {
19     for (int i = inLeft; i < inRight; i++)
20         if (inOrder[i] == val)
21             return i;
22 }
23 
24 Node* ConstructTree(int postLeft, int postRight, int inLeft, int inRight)
25 {
26     if (postLeft == postRight)
27         return nullptr;
28 
29     Node* root = new Node;
30     root->val = postOrder[postRight-1];
31     int index = InOrderFindIndex(root->val, inLeft, inRight);
32     int leftLength = index - inLeft;
33     int rightLength = inRight - index - 1;
34     root->left = ConstructTree(postLeft, postLeft + leftLength, inLeft, index);
35     root->right = ConstructTree(postLeft + leftLength, postRight - 1, index + 1, inRight);
36 
37     return root;
38 }
39 
40 void LevelOrderTraversal(Node* root, int NodeNum)
41 {
42     queue<Node*> que;
43     que.push(root);
44     int cnt = 0;
45     while (!que.empty())
46     {
47         Node* last = que.front();
48         que.pop();
49         cout << last->val;
50         ++cnt;
51         if (cnt < NodeNum)
52             cout << " ";
53         if (last->left)
54             que.push(last->left);
55         if (last->right)
56             que.push(last->right);
57     }
58 
59     
60 }
61 
62 int main()
63 {
64     int NodeNum;
65     cin >> NodeNum;
66 
67     for (int i = 0; i < NodeNum; i++)
68         cin >> postOrder[i];
69     for (int i = 0; i < NodeNum; i++)
70         cin >> inOrder[i];
71 
72     Node* root;
73 
74     root = ConstructTree(0, NodeNum, 0, NodeNum);
75     LevelOrderTraversal(root, NodeNum);
76 }

 

posted @ 2015-08-07 00:19  JackWang822  阅读(188)  评论(0)  编辑  收藏  举报