307. Range Sum Query - Mutable

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307. Range Sum Query - Mutable

Description

Given an integer array nums, handle multiple queries of the following types:

  • Update the value of an element in nums.
  • Calculate the sum of the elements of nums between indices left and right inclusive where left <= right.

Implement the NumArray class:

  • NumArray(int[] nums) Initializes the object with the integer array nums.
  • void update(int index, int val) Updates the value of nums[index] to be val.
  • int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]).

Example 1:

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Input

["NumArray", "sumRange", "update", "sumRange"]
[[[1, 3, 5]], [0, 2], [1, 2], [0, 2]]
Output

[null, 9, null, 8]

Explanation

NumArray numArray = new NumArray([1, 3, 5]);
numArray.sumRange(0, 2); // return 1 + 3 + 5 = 9
numArray.update(1, 2);   // nums = [1, 2, 5]
numArray.sumRange(0, 2); // return 1 + 2 + 5 = 8

Constraints:

  • 1 <= nums.length <= 3 * 10^4
  • -100 <= nums[i] <= 100
  • 0 <= index < nums.length
  • -100 <= val <= 100
  • 0 <= left <= right < nums.length
  • At most 3 * 10^4 calls will be made to update and sumRange.

Hints/Notes

Solution

Language: C++

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class NumArray {
private:
    vector<int> nums;
    vector<int> tree;

    int preSum(int t) {
        int sum = 0;
        for (; t > 0; t -= (t & -t)) {
            sum += tree[t];
        }
        return sum;
    }

public:
    NumArray(vector<int>& nums) :nums(nums.size()), tree(nums.size() + 1) {
        for (int i = 0; i < nums.size(); i++) {
            update(i, nums[i]);
        }
    }

    void update(int index, int val) {
        int delta = val - nums[index];
        nums[index] = val;
        for (int i = index + 1; i < tree.size(); i += (i & -i)) {
            tree[i] += delta;
        }
    }

    int sumRange(int left, int right) {
        return preSum(right + 1) - preSum(left);
    }
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * obj->update(index,val);
 * int param_2 = obj->sumRange(left,right);
 */