leetcode 226 Invert Binary Tree

题目连接

https://leetcode.com/problems/invert-binary-tree/ 

Invert Binary Tree

Description

Invert a binary tree.

     4
   /   
  2     7
 /    / 
1   3 6   9

to

     4
   /   
  7     2
 /    / 
9   6 3   1

/**
 * 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 {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(!root) return nullptr;
        function<void(TreeNode*)> dfs = [&](TreeNode *root) {
            if(!root) return;
            swap(root->left, root->right);
            dfs(root->left);
            dfs(root->right);
        };
        dfs(root);
        return root;
    }
};