26. Count Divisors

Pattern: Math (O(1))

Problem

Given A, B, K, return count of integers in [A, B] divisible by K.

Example:

Input:  A = 6, B = 11, K = 2
Output: 3  // 6, 8, 10

Solution

func countDivisors(a, b, k int) int {
    res := b/k - a/k
    if a%k == 0 {
        res++
    }
    return res
}

O(1) — no loops needed.