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 {

    private static int[] a;
    private static int i = 0;

    // root 为null不可能进来
    private static void dfs(TreeNode root) {
        
        if (root.left != null) {
            dfs(root.left);
        }
        

        if (root.right != null) {
            dfs(root.right);
        }
		
		// 节点放到后面
		a[i++] = root.val;
    }

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

        if (root == null) {
            return new int[0];
        } else {
            a = new int[100];
            i = 0;
            dfs(root);
            int[] b = Arrays.copyOf(a, i);
            return b;
        }

    }
}