Modified Binary Search

binarySearchFirstAndLast.js

function binarySearch(arr, k, searchType) {
  let left = 0;
  let right = arr.length - 1;

  let ans = null;

  while (left <= right) {
    const midIdx = Math.floor((left + right) / 2);

    const el = arr[midIdx];

    if (el === k) {
      ans = midIdx;

      if (searchType === SEARCH_TYPE.FIRST) {
        right = midIdx - 1;
      } else {
        left = midIdx + 1;
      }
    } else if (el > k) {
      right = midIdx - 1;
    } else if (el < k) {
      left = midIdx + 1;
    }
  }

  return ans;
}