GFG003.cpp

/*
Indexes of Subarray Sum

Given an array arr[] containing only non-negative integers, your task is to find a continuous subarray (a contiguous sequence of elements) whose sum equals a specified value target. You need to return the 1-based indices of the leftmost and rightmost elements of this subarray. You need to find the first subarray whose sum is equal to the target.

Note: If no such array is possible then, return [-1].

Examples:

Input: arr[] = [1, 2, 3, 7, 5], target = 12
Output: [2, 4]
Explanation: The sum of elements from 2nd to 4th position is 12.
Input: arr[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], target = 15
Output: [1, 5]
Explanation: The sum of elements from 1st to 5th position is 15.
Input: arr[] = [5, 3, 4], target = 2
Output: [-1]
Explanation: There is no subarray with sum 2.

*/

class Solution {
  public:
    vector<int> subarraySum(vector<int> &arr, int target) {
        // code here
        int left = 0, right = 0;
        std::vector<int> result;
        int sum = 0;
        
        while (right < arr.size()) {
           
           sum +=  arr[right];
           
           while (sum > target && left <= right) {
               sum -= arr[left];
               left++;
           }
           
           if (sum == target) {
               result = {left + 1, right + 1};
               return result;
           }
           
           right++;
        }
        
        return {-1};
    }
};