LeetCode-in-Java

779. K-th Symbol in Grammar

Medium

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

@SuppressWarnings("java:S1172")
public class Solution {
    /*
     * Time: O(logn)
     * Space: O(1)
     */
    public int kthGrammar(int n, int k) {
        return Integer.bitCount(k - 1) % 2;
    }
}

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