[leetCode刷题笔记]199. Binary Tree Right Side View

这道题不难，但是要掌握技巧。用recursion来。 递归时记下树的深度，当深度等于list的大小时候加入到list里面，并且优先遍历右子树。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<Integer> rightSideView(TreeNode root) {        List<Integer> view = new ArrayList<Integer>();        helper(root, view, 0);        return view;            }    private void helper(TreeNode root, List<Integer> view, int deep) {        if (root == null) return;        if (view.size() == deep) view.add(root.val);                helper(root.right, view, deep + 1);        helper(root.left, view, deep + 1);    }}