方法1:递归
时间复杂度:$O(n)$
空间复杂度:最坏情况$O(n)$,平均情况$O(logn)$
解题思路
二叉树的后序遍历。
Java 代码
/**
* 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> res = new ArrayList<>();
postorder(root, res);
return res;
}
public void postorder(TreeNode root, List res) {
if (root == null) {
return;
}
postorder(root.left, res);
postorder(root.right, res);
res.add(root.val);
}
}