LeetCode-145二叉树的后序遍历(Binary Tree Postorder Traversal)

class TreeNode {
	int val;
	TreeNode left;
	TreeNode right;
	TreeNode(int x) { val = x; }
}
class Solution {
    List<Integer> postorder=new ArrayList<Integer>();
    public List<Integer> postorderTraversal(TreeNode root) {
        if (root==null)
        	return postorder;
        postorderTraversal(root.left);
        postorderTraversal(root.right);
        postorder.add(root.val);
        return postorder;
    }
}