leetcode303 Range Sum Query - Immutable

 """
 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
 """
 """
 两种做法，第一种动态规划
 第二种切片
 """
 class NumArray:

     def __init__(self, nums):
         n = len(nums)
         self.sum = [0]*(n+1)  #!!!self.的使用
         for i in range(1, n+1):
             self.sum[i] = self.sum[i-1] + nums[i-1] #!!!动态规划方程
     def sumRange(self, i, j):
         return self.sum[j+1]-self.sum[i]

 class NumArray(object):

     def __init__(self, nums):
         self.nums = nums  #!!!换成self

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