【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;
}