Codility - CountDiv - 100% solution - O(1)

CountDiv.java

/*
Write a function:

class Solution { public int solution(int A, int B, int K); }

that, given three integers A, B and K, returns the number of integers within the range [A..B] that are divisible by K, i.e.:

{ i : A ≤ i ≤ B, i mod K = 0 }

For example, for A = 6, B = 11 and K = 2, your function should return 3, because there are three numbers divisible by 2 within the range [6..11], namely 6, 8 and 10.

Write an efficient algorithm for the following assumptions:

A and B are integers within the range [0..2,000,000,000];
K is an integer within the range [1..2,000,000,000];
A ≤ B.
*/

class Solution {
    public int solution(int A, int B, int K) {
        int prevCount = A>0 ? (A-1)/K : -1;
        return B/K - prevCount;
    }
}