# Leetcode - Subarray Sum Equals K Solution

Given an array of integers `nums`

and an integer `k`

, return *the total number of continuous subarrays whose sum equals to k*.

**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 * 10`

^{4}`-1000 <= nums[i] <= 1000`

`-10`

^{7}<= k <= 10^{7}

### Solution in Python3

```
class Solution:
def subarraySum(self, nums: List[int], k: int) -> int:
def cummulativeSum(nums):
total = 0
yield 0
for i in nums:
total += i
yield total
seen_counts = Counter()
cummulative_sum = cummulativeSum(nums)
subarray_with_sum_k = 0
for i in cummulative_sum:
pair = i - k
subarray_with_sum_k += seen_counts[pair]
seen_counts[i] += 1
return subarray_with_sum_k
```