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Problem

Subarray Sum Equals K

LeetCode #560Medium
Running prefix + a count hashmap

Given an integer array and an integer k, return the total number of contiguous subarrays whose elements sum to exactly k.

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Brute force · every subarray
▸
1given arr, k
2count = 0
3for start in 0..n−1:
4    sum = 0
5    for end in start..n−1:
6        sum += arr[end]
7        if sum == k: count++
8return count
state
  • k7
  • count0

line 1Count the contiguous subarrays whose elements sum to exactly k = 7. Brute force: fix a start, extend the end, keep a running sum, and tally every time it hits 7.