Create subarray-sum-equals-k.py

Author: kamyu104

Python/subarray-sum-equals-k.py

@@ -0,0 +1,30 @@
+# Time:  O(n)
+# Space: O(n)
+
+# 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(object):
+    def subarraySum(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: int
+        """
+        result = 0
+        accumulated_sum = 0
+        lookup = collections.defaultdict(int)
+        lookup[0] += 1
+        for num in nums:
+            accumulated_sum += num
+            result += lookup[accumulated_sum - k]
+            lookup[accumulated_sum] += 1
+        return result