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

October LeetCoding Challenge 25

Description

K-th Symbol in Grammar

We build a table of n rows (1-indexed). We start by writing 0 in the 1st row. Now in every subsequent row, we look at the previous row and replace each occurrence of 0 with 01, and each occurrence of 1 with 10.

• For example, for n = 3, the 1st row is 0, the 2nd row is 01, and the 3rd row is 0110.

Given two integer n and k, return the kth (1-indexed) symbol in the nth row of a table of n rows.

Example 1:

Input: n = 1, k = 1
Output: 0
Explanation: row 1: 0

Example 2:

Input: n = 2, k = 1
Output: 0
Explanation: 
row 1: 0
row 2: 01

Example 3:

Input: n = 2, k = 2
Output: 1
Explanation: 
row 1: 0
row 2: 01

Constraints:

• 1 <= n <= 30
• 1 <= k <= 2n - 1

Solution

class Solution {
public:
  int kthGrammar(int n, int k) {
    return __builtin_popcount(k - 1) & 1;
  }
};
// @lc code=end

// Accepted
// 55/55 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 53.37 % of cpp submissions (6.2 MB)