averagePair.js

/* Write a function called averagePair. Given a sorted array of integers and a target average, 
 * determine if there is a pair of values in the array where the average of the pair equals the target average. 
 * There may be more than one pair that matches the average target.
 * Time: O(N)
 * Space: O(1) 
 */
const calculateAverageOf2Nums = (num1, num2) => {
  return num1 + num2 / 2;
}

const averagePair = (array, targetAverage) => {
  let leftIndex = 0;
  let rightIndex = array.length - 1;
  while (leftIndex < rightIndex) {
    let average = calculateAverageOf2Nums(array[leftIndex], array[rightIndex]);
    if (average === targetAverage) {
      return true;
    } else if (average < targetAverage) {
      leftIndex++
    } else {
      rightIndex--
    }
  }
  return false;
}

console.log(averagePair([1,2,3],2.5)); // true
console.log(averagePair([1,3,3,5,6,7,10,12,19],8)); // true
console.log(averagePair([-1,0,3,4,5,6], 4.1)); // false 
console.log(averagePair([],4)); // false