Problems/Prefix Sums/Sum Between Range
Prefix Sums
easy

Sum Between Range

The Problematic Playlist problem asks you to find how many song combinations in a playlist have a total length equal to a target duration. This is a common interview problem that tests your understanding of prefix sums and efficient counting techniques.

arrayprefix sumhash mapcountingsubarrays

Problem Statement

You are given an array of integers representing the lengths of songs in a playlist. You are also given a target duration. Your task is to determine the number of distinct contiguous subarrays (sections of the playlist) whose elements sum up to exactly the target duration.

Example 1
Input: [3, 4, 7, 2, -3, 1, 4, 2], target = 7
Output: 4
The subarrays that sum to 7 are [3, 4], [7], [2, -3, 1, 4, 2], and [4, 2, -3, 4]. Therefore, the answer is 4.
Example 2
Input: [1, 2, 3, 4, 5], target = 10
Output: 2
The subarrays that sum to 10 are [1, 2, 3, 4] and [5, 4, 1] when read in reverse order. Therefore, the answer is 2.
Constraints
  • -1 <= array length <= 10^5
  • --10^3 <= array elements <= 10^3
  • --10^7 <= target <= 10^7
  • -Array elements are integers
  • -Target is an integer

Brute Force Approach

The most straightforward way to solve this is to check every possible subarray. Imagine you're trying to find a specific sequence of songs on a playlist. You'd start by checking the first song, then the first two, then the first three, and so on. You'd repeat this process starting from the second song, then the third, and so on, until you've checked every possible combination.

TimeO(n^3)
SpaceO(1)

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