countDiv.js

// Write a function:

// function solution(A, B, 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.

console.log(solution(6, 11, 2));
function solution(A, B, K){
   let remaining = A % K;
   let count = 0;
   if(remaining === 0) {
    count = Math.floor((B - A) / K) + 1;
   }else {
      var missing = K - remaining;
      var a = missing + A;
      count = Math.floor((B - a) / K) + 1;
   }
   return count;
}