题解 | #二叉树的后序遍历#

方法一：递归

/*
 * 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
     */
    List<Integer> list=new ArrayList<>();
    public int[] postorderTraversal (TreeNode root) {
        // write code here
        postOrder(root);
        int[] res= new int[list.size()];
        for(int i=0;i<list.size();i++){
            res[i]=list.get(i);
        }
        return res;
        
    }
    void postOrder(TreeNode root){
        if(root!=null){
            postOrder(root.left);
            postOrder(root.right);
            list.add(root.val);
        }
    }
}