226. Invert Binary Tree

1/**
2 * Definition for a binary tree node.
3 * class TreeNode {
4 *     val: number
5 *     left: TreeNode | null
6 *     right: TreeNode | null
7 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
8 *         this.val = (val===undefined ? 0 : val)
9 *         this.left = (left===undefined ? null : left)
10 *         this.right = (right===undefined ? null : right)
11 *     }
12 * }
13 */
14
15function invertTree(root: TreeNode | null): TreeNode | null {
16    if(root === null) return null;
17    const left = invertTree(root.left);
18    const right = invertTree(root.right);
19    
20    root.left = right;
21    root.right = left;
22    return root;
23};