Is Range Sum Query - Immutable easy or hard?

Range Sum Query - Immutable is categorized as an Easy problem on LeetCode with an acceptance rate above 70%. The main concept is understanding prefix sums and recognizing when preprocessing can reduce repeated work in multiple queries.

How to solve Range Sum Query - Immutable in O(n)?

Build a prefix sum array where each index stores the cumulative sum up to that position. After this O(n) preprocessing step, compute any range sum in constant time using subtraction of prefix values. This converts repeated summation work into simple arithmetic lookups.

Range Sum Query - Immutable Python or Java solution?

Most implementations create a prefix array during object initialization and compute sums in the sumRange function. Python, Java, C++, and JavaScript solutions all follow the same logic: preprocess cumulative sums once and answer queries with constant-time subtraction.

What is the best approach for Range Sum Query - Immutable?

The prefix sum array approach is the most efficient for this problem. Precompute cumulative sums in O(n) time, then answer each range query in O(1) using prefix[right] - prefix[left-1]. Because the array never changes, prefix sums eliminate repeated scanning of elements.

What data structure is used in Range Sum Query - Immutable?

The most common structure is a prefix sum array that stores cumulative totals for fast lookups. A segment tree can also be used for range queries, though it is typically unnecessary when the array is immutable and updates are not required.

What is the time complexity of Range Sum Query - Immutable?

Using the optimal prefix sum solution, preprocessing takes O(n) time and each query runs in O(1). The brute force method requires O(n) time per query, while a segment tree answers queries in O(log n) after O(n) preprocessing.

Is Range Sum Query - Immutable asked at Google, Amazon, or Meta?

Range query problems using prefix sums appear frequently in interviews at companies like Amazon, Google, and Meta. The exact problem may vary, but the prefix sum technique is a common pattern used in array and subarray sum questions.

Description Solution Video 7:42

303. Range Sum Query - Immutable

Easy73.5% acceptance8 companies

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

Explanation
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: