Leetcode 307. Range Sum Query - Mutable (Python)

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题目大意

构建一个数据结构，共有两种操作方式

sumRange(i，j)：计算[i,j]范围内数组和
update(i,val)：将位于数组坐标i的元素值改为val

算法

使用线段树即可

代码

class Segment_Tree(object):    def add(self,start,end,llist):        self.start = start        self.end = end        self.middle = (start+end)/2        self.num = 0        if self.start + 1 == self.end:            self.num = llist[self.start]            return self.num        else:            left = Segment_Tree()            self.left = left            self.num += left.add(start,self.middle,llist)            right = Segment_Tree()            self.right = right            self.num += right.add(self.middle,end,llist)            return self.num    def update(self,index,num):        if self.start == index and self.start + 1 == self.end:            cha = num - self.num            self.num = num            return cha        if index >= self.middle:            cha = self.right.update(index,num)            self.num += cha            return cha        else:            cha = self.left.update(index,num)            self.num += cha            return cha    def sum(self,start,end):        if start == self.start and end == self.end:            return self.num        if end <= self.middle:            return self.left.sum(start,end)        elif start>= self.middle:            return self.right.sum(start,end)        else:            left_val = self.left.sum(start,self.middle)            right_val = self.right.sum(self.middle,end)            return left_val + right_valclass NumArray(object):    def __init__(self, nums):        """        initialize your data structure here.        :type nums: List[int]        """        if len(nums) == 0:            nums.append(0)        self.nums = nums        self.st = Segment_Tree()        self.st.add(0,len(self.nums),self.nums)    def update(self, i, val):        """        :type i: int        :type val: int        :rtype: int        """        self.st.update(i,val)        return val    def sumRange(self, i, j):        """        sum of elements nums[i..j], inclusive.        :type i: int        :type j: int        :rtype: int        """        return self.st.sum(i,j+1)

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