lib/medium/560_subarray_sum_equals_k.rb

# frozen_string_literal: true

# https://leetcode.com/problems/subarray-sum-equals-k/
# @param {Integer[]} nums
# @param {Integer} k
# @return {Integer}
def subarray_sum(nums, k)
  result = 0
  pre = 0
  values = {}
  values[0] = 1

  nums.each do |num|
    pre += num
    result += values.fetch(pre - k, 0)
    values[pre] = values.fetch(pre, 0) + 1
  end

  result
end