Binary Tree Right Side View.cpp

/*
Binary Tree Right Side View
===========================

Given the root of 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 1:
Input: root = [1,2,3,null,5,null,4]
Output: [1,3,4]

Example 2:
Input: root = [1,null,3]
Output: [1,3]

Example 3:
Input: root = []
Output: []

Constraints:
The number of nodes in the tree is in the range [0, 100].
-100 <= Node.val <= 100
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution
{
public:
  vector<int> rightSideView(TreeNode *root)
  {
    if (!root)
      return {};
    vector<int> ans;
    queue<TreeNode *> pending;
    pending.push(root);

    while (pending.size())
    {
      TreeNode *end;
      for (int i = pending.size(); i > 0; --i)
      {
        auto curr = pending.front();
        pending.pop();

        end = curr;
        if (curr->left)
          pending.push(curr->left);
        if (curr->right)
          pending.push(curr->right);
      }
      ans.push_back(end->val);
    }
    return ans;
  }
};