145.二叉树的后序遍历.java

import java.util.ArrayList;

/*
 * @lc app=leetcode.cn id=145 lang=java
 *
 * [145] 二叉树的后序遍历
 */

// @lc code=start
/**
 * 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 {
    public List<Integer> postorderTraversal(TreeNode root) {
        List<Integer> ans = new ArrayList<>();
        traversal(root, ans);
        return ans;
    }
    
    void traversal(TreeNode node, List<Integer> list) {
        if (node == null) return;
        traversal(node.left, list);
        traversal(node.right, list);
        list.add(node.val);
    }
}
// @lc code=end