> For the complete documentation index, see [llms.txt](https://soumyajit4419.gitbook.io/ds-algo/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://soumyajit4419.gitbook.io/ds-algo/binary-search/template-iii/4.-find-first-and-last-position-of-element-in-sorted-array.md).

# 4. Find First and Last Position of Element in Sorted Array

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]`.

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]
```

## Solution: (Binary Search)

```cpp
class Solution
{
public:
    int firstOcc(vector<int> &arr, int start, int end, int target)
    {

        while (start <= end)
        {
            int mid = (start + end) / 2;
            if ((mid == 0 || arr[mid - 1] < arr[mid]) && arr[mid] == target)
            {
                return mid;
            }
            else if (target <= arr[mid] )
            {
                end = mid - 1;
            }
            else
            {
                start = mid + 1;
            }
        }
        return -1;
    }

    int lastOcc(vector<int> &arr, int start, int end, int target)
    {

        while (start <= end)
        {
            int mid = (start + end) / 2;
            if ((mid == arr.size() - 1 || arr[mid + 1] > arr[mid]) && arr[mid] == target)
            {
                return mid;
            }
            else if (target >= arr[mid])
            {
                start = mid + 1; 
            }
            else
            {
                end = mid - 1;
            }
        }
        return -1;
    }

    vector<int> searchRange(vector<int> &nums, int target)
    {
        vector<int> v;
        int start = firstOcc(nums, 0, nums.size() - 1, target);
        int end = lastOcc(nums, 0, nums.size() - 1, target);
        v.push_back(start);
        v.push_back(end);
        return v;
    }
};
```

**Time Complexity: O(log n)**