303. Range Sum Query - Immutable 数组范围求和 - 不变

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

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

1. You may assume that the array does not change.
2. There are many calls to sumRange function.

class NumArray(object):
    summations = []
    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self.summations = []
        curSum = 0
        for i in nums:
            curSum = curSum + i
            self.summations.append(curSum)
        
    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        if i is 0:
            return self.summations[j]
        else:
            return self.summations[j] - self.summations[i-1]

来自为知笔记(Wiz)