0226-invert-binary-tree.cpp

/*
 Given the root of a binary tree, invert the tree, and return its root
 Ex. root = [4,2,7,1,3,6,9] -> [4,7,2,9,6,3,1], [2,1,3] -> [2,3,1]

 Preorder traversal, at each node, swap it's left and right children

 Time: O(n)
 Space: O(n)
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode() : val(0), left(nullptr), right(nullptr) {}
 * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
*/
classSolution {
public:
 TreeNode* invertTree(TreeNode* root) {
if (root == NULL) {
returnNULL;
 }
swap(root->left, root->right);
invertTree(root->left);
invertTree(root->right);
return root;
 }
};