题目
描述
给出一棵二叉树,返回其后序遍历
样例
给出二叉树 {1,#,2,3},
1
\
2
/
3
返回 [3,2,1].
解答
思路
后序遍历二叉树
代码
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: Postorder in ArrayList which contains node values.
*/
public ArrayList<Integer> postorderTraversal(TreeNode root) {
// write your code here
ArrayList<Integer> a = new ArrayList<Integer>();
postOrder(a, root);
return a;
}
private void postOrder(ArrayList<Integer> a, TreeNode root){
if(root == null) return;
postOrder(a, root.left);
postOrder(a, root.right);
a.add(root.val);
}
}