34. Find First and Last Position of Element in Sorted Array

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]

Constraints:

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109
• nums is a non-decreasing array.
• -109 <= target <= 109

Solution:

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
  if (nums.length === 1 && nums[0] === target) return [0, 0];
  if (nums.length === 0) return [-1, -1];

  var l = 0;
  var r = nums.length - 1;
  var foundStart = -1;
  var foundEnd = -1;

  while (l <= r) {
    if (nums[l] === target && foundStart === -1) {
      foundStart = l;

      if (nums[r] === nums[foundStart]) {
        foundEnd = r;
        break;
      }
    } else if (foundStart !== -1) {
      var m = ((l + r) / 2) ^ 0;
      if (target > nums[m]) {
        l = m + 1;
      } else if (target < nums[m]) {
        r = m - 1;
      } else if (target === nums[m]) {
        foundEnd = m;
        l = m + 1;
      } else l++;
    } else l++;
  }

  if (foundStart !== -1 && foundEnd === -1) foundEnd = foundStart;
  return [foundStart, foundEnd];
};