LeetCode 199. 二叉树的右视图(Binary Tree Right Side View)

199. 二叉树的右视图
199. Binary Tree Right Side View

题目描述
给定一棵二叉树，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

LeetCode199. Binary Tree Right Side View

示例:

输入: [1,2,3,null,5,null,4] 输出: [1, 3, 4] 解释: ``` 1 <--- / 2 3 <--- 5 4 <--- ```

The core idea of this algorithm:

1. Each depth of the tree only select one node. 2. View depth is current size of result list.

Java 实现

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

import java.util.ArrayList;
import java.util.List;

class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        rightView(root, result, 0);
        return result;
    }

    public void rightView(TreeNode curr, List<Integer> result, int currDepth) {
        if (curr == null) {
            return;
        }
        if (currDepth == result.size()) {
            result.add(curr.val);
        }
        rightView(curr.right, result, currDepth + 1);
        rightView(curr.left, result, currDepth + 1);
    }
}

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