LC145.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private List<Integer> postOrderTraversed = new ArrayList<>();

    public List<Integer> postorderTraversal(TreeNode root) {
        traversal(root);
        return postOrderTraversed;
    }

    private void traversal(TreeNode node) {
            if(node == null) return;

            traversal(node.left);
            traversal(node.right);
            postOrderTraversed.add(node.val);
        }
}

//Solved