Create subarray-sum-equals-k.cpp

Author: kamyu104

C++/subarray-sum-equals-k.cpp

@@ -0,0 +1,18 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int subarraySum(vector<int>& nums, int k) {
+        auto result{0};
+        auto accumulated_sum{0};
+        unordered_map<int, int> lookup;
+        ++lookup[0];
+        for (const auto& num : nums) {
+            accumulated_sum += num;
+            result += lookup[accumulated_sum - k];
+            ++lookup[accumulated_sum];
+        }
+        return result;
+    }
+};