find the maximum sum of temperatures of K consecutive days

Thailand is a tropical country. Thai people usually say that Thailand has 3 seasons: Hot Summer, Hotter Summer, and Hottest Summer. It especially feels very hot when you have many consecutive days with high temperatures.
You are planning a K-day trip to Thailand. Since you would like to experience the real Thai Summer, you want your stay to be as hot as possible.
You are given a list of forecasted temperatures of N consecutive days. You would like to find the maximum sum of temperatures of K consecutive days. It is guaranteed that 1 <= K <= N.

Implement 

You are to implement procedure maxk(N,T,K) that returns the maximum sum of temperatures of any K consecutive days, where N is the number of days and T is an array of positive integers where T[i], for 0 <= i < N, is the temperature of day i.

Example

Suppose that N=6, K=3 and T = 10 50 30 20 5 1.

There are 4 possible 3-day trips, starting from day 0, day 1, day 2, and day 3; and their sum of temperatures are 90, 100, 55, and 26. Therefore, procedure maxk should return 100.

Subtasks

Subtask 1

• N <= 1 000, 0 < T[i] <= 1 000

Subtask 2

• N <= 1 000 000, 0 < T[i] <= 1 000