Since all elements are non-negative, we can use the sliding window (two-pointer) technique. We maintain a window [start, end] and its current_sum. If current_sum is less than target, we expand the window by moving end. If it's more, we contract it by moving start.

1. Initialize start = 0 and current_sum = 0.
2. Iterate end from 0 to n-1:
   • Add nums[end] to current_sum.
   • While current_sum > target and start < end:
     • Subtract nums[start] from current_sum.
     • Increment start.
   • If current_sum == target:
     • Return [start, end].
3. If loop ends without finding the target, return [-1, -1].

• Time Complexity: O(N), as each element is added and removed from the window at most once.
• Space Complexity: O(1), only a few scalar variables.

def subarray_sum(nums, target):
    start = 0
    current_sum = 0
    
    for end in range(len(nums)):
        current_sum += nums[end]
        
        while current_sum > target and start < end:
            current_sum -= nums[start]
            start += 1
            
        if current_sum == target:
            return [start, end]
            
    return [-1, -1]