We use a sliding window with two pointers. We increment the right pointer to add elements until the sum >= target, then increment the left pointer to find the minimum length.

1. l = 0, curr_sum = 0, res = float('inf').
2. For each r, curr_sum += nums[r].
3. While curr_sum >= target:
   • res = min(res, r - l + 1).
   • curr_sum -= nums[l].
   • l += 1.
4. Return res if it was modified, else 0.

• Time Complexity: O(N).
• Space Complexity: O(1).

def min_sub_array_len(target, nums):
    l = 0
    curr_sum = 0
    res = float('inf')
    
    for r in range(len(nums)):
        curr_sum += nums[r]
        while curr_sum >= target:
            res = min(res, r - l + 1)
            curr_sum -= nums[l]
            l += 1
            
    return res if res != float('inf') else 0