leetcode199二叉树的右视图

Posted 2021-09-05 lisin-lee-cooper

一.问题描述

给定一个二叉树的 根节点 root，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。

输入: [1,2,3,null,5,null,4]
输出: [1,3,4]

二.示例代码

public class BSTRightView199 {

    public static void main(String[] args) {
        TreeNode treeNode1 = new TreeNode(1);
        TreeNode treeNode2 = new TreeNode(2);
        TreeNode treeNode3 = new TreeNode(3);
        TreeNode treeNode5 = new TreeNode(5);
        TreeNode treeNode4 = new TreeNode(4);

        treeNode1.left = treeNode2;
        treeNode1.right = treeNode3;
        treeNode2.right = treeNode5;
        treeNode3.right = treeNode4;

        List<Integer> result = BSTRightView(treeNode1);
        System.out.println(result);
    }

    public static List<Integer> BSTRightView(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        rightPreOrder(root, 0, result);
        return result;
    }

    public static void rightPreOrder(TreeNode node, int depth, List<Integer> ans) {
        if (node != null) {
            if (depth == ans.size()) {
                ans.add(node.val);
            }
            rightPreOrder(node.right, depth + 1, ans);
            rightPreOrder(node.left, depth + 1, ans);
        }
    }

}