I'm busy playing Dungeons & Fighters, so won't do pick up.

Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 20

Description

Binary Tree Level Order Traversal

Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]

Example 2:

Input: root = [1]
Output: [[1]]

Example 3:

Input: root = []
Output: []

Constraints:

• The number of nodes in the tree is in the range [0, 2000].
• -1000 <= Node.val <= 1000

Solution

class Solution {
public:
  vector<vector<int>> levelOrder(TreeNode* root) {
    if(!root) return {};
    queue<TreeNode*> q;
    vector<vector<int>> answer;
    q.push(root);
    while(q.size()) {
      int sz = q.size();
      vector<int> curLevel;
      for(int i = 0; i < sz; ++i) {
        auto node = q.front();
        q.pop();
        curLevel.push_back(node->val);
        if(node->left) {
          q.push(node->left);
        }
        if(node->right) {
          q.push(node->right);
        }
      }
      answer.push_back(curLevel);
    }
    return answer;
  }
};