LeetCode-in-All
560. Subarray Sum Equals K
Medium
Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.
A subarray is a contiguous non-empty sequence of elements within an array.
Example 1:
Input: nums = [1,1,1], k = 2
Output: 2
Example 2:
Input: nums = [1,2,3], k = 3
Output: 2
Constraints:
1 <= nums.length <= 2 * 104-1000 <= nums[i] <= 1000-107 <= k <= 107
Solution
defmodule Solution do
@spec subarray_sum(nums :: [integer], k :: integer) :: integer
def subarray_sum(nums, k) do
nums |> Enum.reduce({0, 0, %{0 => 1}}, fn n, {ans, pre_sum, map} ->
pre_sum = pre_sum + n
ans = ans + Map.get(map, pre_sum - k, 0)
{ans, pre_sum, Map.update(map, pre_sum, 1, &(&1 + 1))}
end)
|> elem(0)
end
end