Longest Window Within Budget

Problem

Each day of a trip has a cost, and neither the costs nor the budget are ever negative. Given the list of daily costs and the budget, return the length of the longest run of consecutive days whose costs add up to at most the budget. If every single day is over budget on its own, return 0.

Examples

Input:  costs = [4, 1, 1, 3, 2, 6], budget = 6
Output: 3
Why:    days 1-3 cost 1 + 1 + 3 = 5, and no run of four days fits

Input:  costs = [0, 0, 2, 0], budget = 0
Output: 2
Why:    the two free days at the start are the longest run that costs nothing

Input:  costs = [9, 8], budget = 5
Output: 0
Why:    edge case, every single day is already over budget

Hints

0 / 3

1. Hint 1reveal
2. Hint 2locked
3. Hint 3locked

def longest_within(costs, budget):
    left = total = best = 0
    for right, cost in enumerate(costs):
        total += cost
        while total > budget:           # shrink until the window fits again
            total -= costs[left]
            left += 1
        best = max(best, right - left + 1)
    return best

print(longest_within([4, 1, 1, 3, 2, 6], 6))  # -> 3
print(longest_within([0, 0, 2, 0], 0))        # -> 2
print(longest_within([9, 8], 5))              # -> 0