invert-binary-tree.cpp

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