lleetcode 307. Range Sum Query - Mutable树状数组

最新推荐文章于 2021-06-03 17:50:58 发布

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本文介绍了一种高效的数据结构实现方法，用于处理数组中指定区间的元素求和及元素值更新操作。通过使用该方法，可以实现在数组被修改的情况下快速计算任意区间内元素的总和。

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

The update(i, val) function modifies nums by updating the element at index i to val.

Example:

Given nums = [1, 3, 5]

sumRange(0, 2) -> 9
update(1, 2)
sumRange(0, 2) -> 8

Note:

The array is only modifiable by the update function.

You may assume the number of calls to update and sumRange function is distributed evenly.


class NumArray(object):
    def __init__(self, nums):
        self.n = len(nums)
        self.c = [0] * (self.n+1)
        self.nums = [0] * (self.n+1)
        for i in range(0 , self.n):
            self.update(i , nums[i])

    def lowbit(self , x):
        return x & (-x)

    def update(self, i, val):
        dif = val - self.nums[i]
        self.nums[i] = val
        i += 1
        while i <= self.n:
            self.c[i] += dif
            i += self.lowbit(i)

    def sumPrefix(self , i):
        sum = 0
        i += 1
        while i > 0 :
            sum += self.c[i]
            i -= self.lowbit(i)
        return sum

    def sumRange(self, i, j):
        return self.sumPrefix(j) - self.sumPrefix(i-1)

if __name__ == '__main__':
    obj = NumArray([1, 3, 5])
    print(obj.sumRange(0 , 2))
    obj.update(1 , 2)
    print(obj.sumRange(0, 2))