【07_226】Invert Binary Tree

Invert Binary Tree

Total Accepted: 54994 Total Submissions: 130742 Difficulty: Easy

Invert a binary tree.

     4
   /   \
  2     7
 / \   / \
1   3 6   9

to

     4
   /   \
  7     2
 / \   / \
9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

 

 

通过这道题，好好理解了递归。

递归返回的是什么要考虑清楚，

可以仔细研磨这道题，很好的题。

 

 

C语言

 /**
  * Definition for a binary tree node.
  * struct TreeNode {
  *     int val;
  *     struct TreeNode *left;
  *     struct TreeNode *right;
  * };
  */
 struct TreeNode* invertTree(struct TreeNode* root) {
     if (root == NULL)
         return root;
     if (root->left == NULL && root->right == NULL)
         return root;
     else{
         struct TreeNode* temp = root->right;
         root->right = root->left;
         root->left = temp;
     }
     root->left = invertTree(root->left);
     root->right = invertTree(root->right);

     return root;
 }

下面是在网上找的一种解法，C++写的。由于这是对实际树的结构进行操作，所以说可以不特别管返回值。

 TreeNode* invertTree(TreeNode* root) {
     if (root) {
         invertTree(root->left);
         invertTree(root->right);
         std::swap(root->left, root->right);
     }
     return root;
 }