#226.Invert Binary Tree [LeetCode Grind 75 in Java]

class Solution {
    public void invert(TreeNode root){
        if(root == null) return;

        //swap children
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;

        invert(root.left);
        invert(root.right);

    }
    public TreeNode invertTree(TreeNode root) {
        invert(root);
        return root;
    }
}