LeetCode 303. Range Sum Query - Immutable

'''
Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Key is the calculation efficiency.
'''

class NumArray1(object):
#1088 ms, 15.3 MB
    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self.nums = nums

    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        return sum(self.nums[i:j+1])


# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)

class NumArray(object):
#144ms, 15.3MB
    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self.list = []
        total = 0
        for i in nums:
            total += i
            self.list.append(total)
           
    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        if i == 0:
            return self.list[j]
        else:
            return self.list[j] - self.list[i-1]