C ++ _ Learning Essay_Reconstruction of binary tree and judge whether it is symmetric binary tree

The binary tree is reconstructed by inputting the preorder traversal and midorder traversal of the binary tree,

Then judge whether the binary tree is a symmetric binary tree.

1 #include <iostream>
 2 #include <vector>
 3  using  namespace std;
 4  
5  struct TreeNode {
 6      int val;
 7      TreeNode * left;
 8      TreeNode * right;
 9      TreeNode ( int x): val (x), left ( NULL), right (NULL) {}
 10  };
 11  
12  // Reconstruct a binary tree according to pre-order traversal and mid-order traversal 
13 TreeNode * reConstructBinaryTree (vector < int > pre, vector < int > vin) {
 14      if (pre. empty () ||vin.empty ())
 15          return nullptr;
 16      // Root node 
17      TreeNode * root = new TreeNode (pre [ 0 ]);
 18      int root_index = 0 ;
 19      // Find the index value of the root node 
20      for ( int i = 0 ; i <pre.size (); i ++ ) {
 21          if (vin [i] == pre [ 0 ]) {
 22              root_index = i;
 23              break ;
 24          }
 25      }
 26      vector <int> pre_left, pre_right, vin_left, vin_right;
27     for (int i = 0; i < root_index; i++) {
28         pre_left.push_back(pre[i + 1]);
29         vin_left.push_back(vin[i]);
30     }
31 
32     for (int i = root_index + 1; i < pre.size(); i++) {
33         pre_right.push_back(pre[i]);
34         vin_right.push_back(vin[i]);
35     }
36 
37     root->left = reConstructBinaryTree(pre_left, vin_left);
38     root->right = reConstructBinaryTree(pre_right, vin_right);
39 
40     return root;
41 }
42 
43 
44 //判断是否是对称的
45 bool isSymmetrical(TreeNode* p1, TreeNode* p2) {
46     if (p1 == NULL && p2 == NULL)
47         return true;
48     if (p1 == NULL || p2 == NULL)
49         return false;
50     if (p1->val != p2->val)
51         return false;
52     return isSymmetrical(p1->left, p2->right) && isSymmetrical(p1->right, p2->left);
53 }
54 
55 
56 bool isSymmetrical(TreeNode* pRoot) {
57     if (pRoot == NULL) {
58         return true;
59     }
60     return isSymmetrical(pRoot, pRoot);
61 }
62 
63 
64 int main() {
65     vector<int> pre, vin;
66     cout << "请输入节点数：" << endl;
 67      int n = 0 , temp;
 68      cin >> n;
 69      cout << " Please enter the preorder traversal: " << endl;
 70      for ( int i = 0 ; i <n; i ++ ) {
 71          cin >> temp;
 72          pre.push_back (temp);
 73      }
 74      cout << " Please enter the middle sequence traversal: " << endl;
 75      for ( int i = 0 ; i <n;i++) {
76         cin >> temp;
77         vin.push_back(temp);
78     }
79     bool is;
80     TreeNode* root_node = reConstructBinaryTree(pre, vin);
81     is = isSymmetrical(root_node);
82     cout << is;
83     
84 }

 

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Reference link:

https://www.cnblogs.com/wanglei5205/p/8503036.html

https://cuijiahua.com/blog/2018/01/basis_58.html