This solution is not a O(N) look at the comment "# No O(N) cause", i don't know why, can't use "nums[0]" before loop, i got error out of range, so stranger!

```
def __init__(self, nums):
"""
initialize your data structure here.
:type nums: List[int]
"""
self.lists = [0]
# error out of range when use nums[0] here
# nums[0]
for i, n in enumerate(nums):
# No O(N) cause
if i == 0:
self.lists.append(nums[i])
else:
self.lists.append(self.lists[i] + n)
def sumRange(self, i, j):
"""
sum of elements nums[i..j], inclusive.
:type i: int
:type j: int
:rtype: int
"""
return self.lists[j+1] - self.lists[i]
```