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Subarray Sum Equals K

Medium
VerifiedArrayHash MapPrefix Sum~25 min

Given nums and an integer k, return the count of contiguous subarrays whose elements sum to k. Values may be negative, so a sliding window will not work.

Track prefix sums in a hash map. The input arrives as a single object { nums, k }.

Examples

in{ nums: [1, 1, 1], k: 2 }
out2

[1,1] appears at indices 0..1 and 1..2.

in{ nums: [1, 2, 3], k: 3 }
out2

[1,2] and [3] both sum to 3.

Constraints

  • 1 ≤ nums.length ≤ 2 × 10⁴
  • -1000 ≤ nums[i] ≤ 1000
  • -10⁷ ≤ k ≤ 10⁷
  • Target: O(n) time.

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