作用

1. 单点修改
2. 区间查询

代码模版

from typing import List
class NumArray:

    def __init__(self, nums: List[int]):
        self.nums = nums
        self.preNums = [0]*(len(nums)+1)
        for i in range(len(nums)):
            self.add(i+1,nums[i])

    # 从左到右获取第一个1
    def lowbit(self,index:int)->int:
        return index & -index
        
    # 生成数组
    def add(self,index:int, val:int):
        while index < len(self.preNums):
            self.preNums[index] += val
            index+= self.lowbit(index)

    # 计算和
    def preSum(self,index:int)->int:
        result = 0 
        while index:
            result += self.preNums[index]
            index -= self.lowbit(index)
        return result

    # 单点修改
    def update(self, index: int, val: int) -> None:
        self.add(index + 1, val - self.nums[index])
        self.nums[index] = val

    # 获取范围和
    def sumRange(self, left: int, right: int) -> int:
        return self.preSum(right + 1) - self.preSum(left)