README.md

779. K-th Symbol in Grammar

On the first row, we write a 0. 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.

Given row N and index K, return the K-th indexed symbol in row N. (The values of K are 1-indexed.) (1 indexed).

Example:
Input: N = 1, K = 1
Output: 0

Input: N = 2, K = 1
Output: 0

Input: N = 2, K = 2
Output: 1

Input: N = 4, K = 5
Output: 1

Explanation:
row 1: 0
row 2: 01
row 3: 0110
row 4: 01101001

Note:

1. N will be an integer in the range [1, 30].
2. K will be an integer in the range [1, 2^(N-1)].

Solutions (Rust)

1. Recursion

impl Solution {
    pub fn kth_grammar(n: i32, k: i32) -> i32 {
        if n <= 2 {
            k - 1
        } else if k > 2_i32.pow(n as u32 - 2) {
            1 - Self::kth_grammar(n - 1, k - 2_i32.pow(n as u32 - 2))
        } else {
            Self::kth_grammar(n - 1, k)
        }
    }
}