Sliding Window

def minSubArrayLen(target: int, nums: List[int]) -> int:
    answer = float("inf")
    left = right = 0
    currSum = 0

    # Expand until target found. Shrink until target lost
    while right < len(nums):
        currSum += nums[right]
        right += 1

        while currSum >= target:
            answer = min(answer, right - left)
            currSum -= nums[left]
            left += 1

    return 0 if answer == float("inf") else answer

Time: O(n)

Space: O(1)

def lengthOfLongestSubstring(s: str) -> int:
    cSet = set()
    answer = 0
    left = 0

    # Expand window
    for right in range(len(s)):
        # Shrink window if duplicate found
        while s[right] in cSet:
            cSet.remove(s[left])
            left += 1

        cSet.add(s[right])
        answer = max(answer, right - left + 1)

    return answer

Time: O(n)

Space: O(n)