leetcode 226 Invert Binary Tree

原题链接：https://leetcode.com/problems/invert-binary-tree/

Description

Invert a binary tree.

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

to

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

Solution

/** * 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;    }};