Subarray with given sum

Given an unsorted array A of size N that contains only non-negative integers, find a continuous sub-array which adds to a given number S.

In case of multiple subarrays, return the subarray which comes first on moving from left to right.

• Time : O(n)
• Space : O(1)

c++

class Solution
{
    public:
    //Function to find a continuous sub-array which adds up to a given number.
    vector<int> subarraySum(int arr[], int n, long long s)
    {
        int l = 0, r = 0;
        long long sum = 0;
        while(r < n) {
            if(sum > s) {
                sum -= arr[l++];
            } else if(sum < s) {
                sum += arr[r++];
            }
            if(sum == s) return {l + 1, r};
        }
        while(sum != s and l < n) {
            sum -= arr[l++];
        }
        if(sum == s) return {l + 1, r};
        
        return {-1};
    }
};