题解 | #二叉树的后序遍历#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型一维数组
     */
    private void recursivelyPostorder(TreeNode vroot, List<Integer> temp){
        if(vroot.left!=null) recursivelyPostorder(vroot.left, temp);
        if(vroot.right !=null) recursivelyPostorder(vroot.right, temp);

        temp.add(vroot.val);
    }

    
    public int[] postorderTraversal (TreeNode root) {
        // write code here

        if(root==null){
            int[] treeList = new int[0];
            return treeList;
        }
        List<Integer> temp = new ArrayList();
        recursivelyPostorder(root, temp);

        int[] treeList = new int[temp.size()];
        for(int i=0;i<temp.size();i++){
            treeList[i] = temp.get(i);
        }

        return treeList;
    }
}