arrayDiff interview question from the Cassidy Williams (cassidoo) newsletter

arrayDiff.js

//Given an array of integers and a target value
//return the number of pairs of array elements
//that have a difference equal to the target value

//arrayDiff([1, 2, 3, 4], 1);
//Result = 3.
// 2 =1 = 1, 3 -2 = 1, 4 -3  = 1;

function arrayDiff(arr, target) {
  return arr.reduce((accumulator, currentValue, currentIndex) => {
    if (currentIndex === arr.length - 1) return accumulator;
    const diff = arr[currentIndex + 1] - currentValue;
    return diff === target ? accumulator + 1 : accumulator;
  }, 0)
}

arrayDiff([1, 2, 3, 4], 1); // 3
arrayDiff([2, 5, 8, 11], 3); // 3
arrayDiff([2, 5, 11, 14], 6); // 1
arrayDiff([], 2); // 0