LeetCode34. JavaScript to find the first and last position of an element in a sorted array

Given an array of integers in ascending order, nums, and a target value, target. Find the starting and ending positions of the given target value in the array.

Your algorithm must be order log n in time.

If no target value exists in the array, return [-1, -1].

Example 1:

Input: nums = [5,7,7,8,8,10] target = 8

Example 2:

Input: nums = [5,7,7,8,8,10], target = 6

Answer reference:

/** * @param {number[]} nums * @param {number} target * @return {number[]} */
var searchRange = function (nums, target) {
    let targetIndex = binarySearch(nums, target, 0, nums.length - 1)
    if (targetIndex == - 1) return [- 1.- 1]
    let l = targetIndex, r = targetIndex
    while(l > 0 && nums[l - 1] == target){
        l--
    }
    while(r < nums.length - 1 && nums[r + 1] == target){
        r++
    }
    return [l, r]
};

function binarySearch(arr, val, lo, hi) {
    if (hi < lo) return - 1
    let mid = lo + parseInt((hi - lo) / 2)

    if (val < arr[mid]) {
        return binarySearch(arr, val, lo, mid - 1)}else if (val > arr[mid]) {
        return binarySearch(arr, val, mid + 1, hi)
    } else {
        return mid
    }
}
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