[Codility] Prefix Sums - CountDiv / Java

1. 문제

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.

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2. 코드

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