226-invert-binary-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.
*/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {TreeNode}
 */

//Recursive Answeer
var invertTree = function(root) {
  //Base Case
  if (root === null) {
    return null;
  }
  //Recursion
  //Save tmp to left part of tree;
  var tmp = root.left;
  //Change the values of root.left to root.right recursively
  root.left = invertTree(root.right);
  //Do the opposite for right but use tmp since its been overwritten
  root.right = invertTree(tmp);

  return root;
};

//Recursive Answer #2
const invertTree = root => {
  //Base case
  if (!root) return null;
  //left and right of tree is turned into an arr, and recurisvely reversed
  [root.left, root.right] = [invertTree(root.right), invertTree(root.left)];
  return root;
};