LEETCODE ALGORITHM:226. Invert Binary Tree

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题目

Invert a binary tree.

Example:

Input:

1
2
3
4
5
     4
   /   \
  2     7
 / \   / \
1   3 6   9

Output:

1
2
3
4
5
     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 f*** off.

题解

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    void invert(TreeNode* root)
    {
        if(root->left!=NULL||root->right!=NULL)
        {
            swap(root->left,root->right);
        }
        if(root->left) invert(root->left);
        if(root->right) invert(root->right);
    }
public:
    TreeNode* invertTree(TreeNode* root) {
        if(root==NULL) return NULL;
        invert(root);
        return root;
    }
};