Maximum Average Subarray I

定长的移动窗口，只要按照rabinKarp一样走for循环就好

class Solution(object):
    def findMaxAverage(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: float
        """
        n = len(nums)
        curSum = sum(nums[:k])
        result = curSum * 1.0 / k
        for i in xrange(n - k + 1):
            result = max(result, curSum * 1.0 / k)
            if i < n - k:
                curSum += nums[i + k]
            curSum -= nums[i]
        return result