303. 区域和检索 - 数组不可变

一、

class NumArray:

    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)

1.sum函数：
二、

class NumArray(object):

    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self._dp=[0]*len(nums)
        sum=0
        for i in range(len(nums)):
            sum+=nums[i]
            self._dp[i]=sum
        

    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        if(i==0):
            return self._dp[j]
        else:
            return self._dp[j]-self._dp[i-1]
# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)

1._var ；变量名前一个下划线来定义，此变量为保护成员protected，只有类及其子类可以访问。此变量不能通过from XXX import xxx 导入
__var;变量名前两个下划线来定义，此变量为私有private，只允许类本身访问，连子类都不可以访问。