Problem
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.
Example:
Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:
1 <---
/ \
2 3 <---
\ \
5 4 <---
Solution (Java)
/**
* 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> rightSideView(TreeNode root) {
List<Integer> list = new ArrayList<>();
recurse(root, 0, list);
return list;
}
private void recurse(TreeNode node, int level, List<Integer> list) {
if (node != null) {
if (list.size() < level + 1) {
list.add(node.val);
}
recurse(node.right, level + 1, list);
recurse(node.left, level + 1, list);
}
}
}
Solution 1 (Javascript)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[]}
*/
var rightSideView = function(root) {
var queue = [{ node: root, level: 0 }];
var result = [];
var now = null;
while (now = queue.shift()) {
if (!now.node) continue;
result[now.level] = now.node.val;
queue.push({ node: now.node.left, level: now.level + 1 });
queue.push({ node: now.node.right, level: now.level + 1 });
}
return result;
};
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).
Solution 2 (Javascript)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[]}
*/
var rightSideView = function(root) {
var result = [];
helper(root, 0, result);
return result;
};
var helper = function (node, level, result) {
if (!node) return;
result[level] = node.val;
helper(node.left, level + 1, result);
helper(node.right, level + 1, result);
};
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).