199

199. Binary Tree Right Side View (Medium)

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       <---

Related Topics:
Tree, Depth-first Search, Breadth-first Search, Recursion, Queue

Similar Questions:

• Populating Next Right Pointers in Each Node (Medium)
• Boundary of Binary Tree (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/binary-tree-right-side-view/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(H)
class Solution {
    vector<int> ans;
    void dfs(TreeNode *root, int lv) {
        if (!root) return;
        if (lv == ans.size()) ans.push_back(root->val);
        else ans[lv] = root->val;
        dfs(root->left, lv + 1);
        dfs(root->right, lv + 1);
    }
public:
    vector<int> rightSideView(TreeNode* root) {
        dfs(root, 0);
        return ans;
    }
};