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Range Sum Query - Immutable⚓︎

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Description⚓︎

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

  • 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.
  • 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:

  • Input
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["NumArray", "sumRange", "sumRange", "sumRange"]
[[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
  • Output
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[null, 1, -1, -3]
  • Explanation
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NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3

Constraints:

  • 1 <= nums.length <= 10^4
  • -10^5 <= nums[i] <= 10^5
  • 0 <= left <= right < nums.length
  • At most 10^4 calls will be made to sumRange.

Solution⚓︎

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class NumArray {
private:
    vector<int> prefixSum;
public:
    NumArray(vector<int>& nums) {
        prefixSum.resize(nums.size() + 1);
        for (int i = 0; i < nums.size(); i++) {
            prefixSum[i + 1] = prefixSum[i] + nums[i];
        }
    }

    int sumRange(int left, int right) {
        return prefixSum[right + 1] - prefixSum[left];
    }
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * int param_1 = obj->sumRange(left,right);
 */