LeetCode 34. Find First and Last Position of Element in Sorted Array (javascript)

Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.

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

Follow up: Could you 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

Idea:

Binary Search

Solution:

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let leftBound = -1;
    let rightBound = -1;
    let l = 0;
    let r = nums.length - 1;
    
    while (l <= r) {
        let mid = l + Math.floor((r - l) / 2);
        if (nums[mid] === target) {
            leftBound = mid;
            r = mid - 1;
        } else if (nums[mid] > target) {
            r = mid - 1;
        } else {
            l = mid + 1;
        }
    }
    
    l = 0;
    r = nums.length - 1;
    while (l <= r) {
        let mid = l + Math.floor((r - l) / 2);
        if (nums[mid] === target) {
            rightBound = mid;
            l = mid + 1;
        } else if (nums[mid] > target) {
            r = mid - 1;
        } else {
            l = mid + 1;
        }
    }
    return [leftBound, rightBound];
};