searchRange.js

/**
Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:
Input: nums = [], target = 0
Output: [-1,-1]
 
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var searchRange = function (nums, target) {
  const binarySearch = (nums, target, isSearchingLeft) => {
    let left = 0;
    let right = nums.length - 1;
    let idx = -1;

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

      if (nums[mid] > target) {
        right = mid - 1;
      } else if (nums[mid] < target) {
        left = mid + 1;
      } else {
        idx = mid;
        if (isSearchingLeft) {
          right = mid - 1;
        } else {
          left = mid + 1;
        }
      }
    }

    return idx;
  };

  const left = binarySearch(nums, target, true);
  const right = binarySearch(nums, target, false);

  return [left, right];
};