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$ curl repovive.com/roadmaps/math-fundamentals/sequences-summations/range-sum-implementation

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$ curl repovive.com/roadmaps/math-fundamentals/sequences-summations/range-sum-implementation

Repovive

Range Sum - Implementation - Sequences & Summations | Math Fundamentals | Repovive

Repovive.

Math Fundamentals18 sections · 842 units13h total

Open in Course

Range Sum - Implementation

In pseudocode

Here's the solution:


class NumArray
    prefix := array

    function constructor(nums)
        n := length of nums
        prefix := array of size n
        prefix[0] := nums[0]
        for i from 1 to n - 1
            prefix[i] := prefix[i - 1] + nums[i]

    function sumRange(i, j)
        if i = 0 then
            return prefix[j]
        else
            return prefix[j] - prefix[i - 1]

The constructor takes $O(n)$ time to build the prefix array. Each query takes $O(1)$ time. This trades space for speed.