0560-Subarray-Sum-Equals-K.py

'''
Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Example 1:
Input:nums = [1,1,1], k = 2
Output: 2
Note:
The length of the array is in range [1, 20,000].
The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].
'''
class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:
        count = summ = 0
        d = {0 : 1}
        for i in range(len(nums)):
            summ += nums[i]
            if summ - k in d:
                count += d[summ - k]
            if summ not in d:
                d[summ] = 1
            else:
                d[summ] += 1
        return count