def __init__(self, nums):
        n = len(nums)
        self.F = [0 for _ in xrange(n+1)]
        for i in xrange(1, n+1):
            self.F[i] = self.F[i-1] + nums[i-1]
initialize your data structure here.
dataset/ETHPy150Open algorhythms/LeetCode/303 Range Sum Query - Immutable.py/NumArray.__init__