http://oj.leetcode.com/problems/binary-tree-postorder-traversal/

Binary Tree Postorder Traversal.java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<Integer> postorderTraversal(TreeNode root) {
        ArrayList<Integer> ret = new ArrayList<Integer>();
        if (root != null){
            ArrayList<Integer> temp = new ArrayList<Integer>();
            if (root.left != null) {
                temp = postorderTraversal(root.left);
                for (Integer each: temp){
                    ret.add(each);
                }
            }
            if (root.right != null) {
                temp = postorderTraversal(root.right);
                for (Integer each: temp){
                    ret.add(each);
                }
            }
            ret.add(root.val);
        }
        return ret;
    }
}