LeetCode-python 303.区域和检索-数组不可变

题目链接
难度：简单       类型： 数组

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给定一个整数数组 nums，求出数组从索引 i 到 j (i ≤ j) 范围内元素的总和，包含 i, j 两点。

示例

给定 nums = [-2, 0, 3, -5, 2, -1]，求和函数为 sumRange()
sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

解题思路

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用另一个数组stack的第i位存储num的前i项和
第k到第j位的和为stack[j]-stack[k-1]

代码实现

class NumArray(object):

    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self.stack = [0]
        for n in nums:
            self.stack.append(self.stack[-1]+n)
        

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


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

本文链接：https://www.jianshu.com/p/65441fae2c3c