Find First and Last Position of Element in Sorted Array

# 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]
 ```

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

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
 var searchRange = function(nums, target) {
    const binarySearch = (start, end) => {
        if (start > end) {
            return [-1, -1];
        }

        const mid = Math.floor((start + end) / 2);
        if (nums[mid] === target) {
            let first = last = mid;
            while(nums[first - 1] === target) {
                first--;
            }
            while(nums[last + 1] === target) {
                last++;
            }
            return [first, last];
        }
        else if (nums[mid] < target) {
            return binarySearch(mid + 1, end);
        } 
        else if (nums[mid] > target) {
            return binarySearch(0, mid - 1);
        } 
    };

    return binarySearch(0, nums.length - 1);
};