O(n) time and O(n) space using Hashtable.

Author: 149ps

560. Subarray Sum Equals K/560. Subarray Sum Equals K.py

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+"""
+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:
+        result,total,hmap = 0,0,{}
+        for num in nums:
+            hmap[total] = hmap.get(total,0) + 1
+            total += num
+            if hmap.get(total-k):
+                result += hmap[total-k]
+        return result