Best K Days in a Row

A shop records its takings each day, and sales[i] is the amount for day i. A day can lose money, so amounts can be negative. Write best_k_days(sales, k) that returns the largest total the shop made over any k days in a row.

Examples

best_k_days([4, 2, 10, 1, 3, 9], 2)   # returns 12
best_k_days([4, 2, 10, 1, 3, 9], 3)   # returns 16
best_k_days([-3, -1, -2], 2)          # returns -3

For three days in a row, the first three days make 4 + 2 + 10 = 16, more than any other stretch of three.

Constraints

• 1 <= k <= len(sales) <= 100,000
• -10^4 <= sales[i] <= 10^4