226. Invert Binary Tree.md

226. Invert Binary Tree

---

leetcode-cn Daily Challenge on September 16th, 2020.

---

Difficulty : Easy

Related Topics : Tree

---

Invert a binary tree.

Example:

Input:

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

Output:

     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.

---

Solution

• mine
  • Java
    • Runtime: 0 ms, faster than 100.00%, Memory Usage: 37.2 MB, less than 22.55% of Java online submissions

      //O(D)time O(1)space
      //D is root deepth
      public TreeNode invertTree(TreeNode root) {
          if(root == null){
              return null;
          }
          TreeNode t = root.left;
          root.left = invertTree(root.right);
          root.right = invertTree(t);
          return root;
      }
      

---