Create subarray-sums-divisible-by-k.cpp

Author: kamyu104

C++/subarray-sums-divisible-by-k.cpp

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+// Time:  O(n)
+// Space: O(k)
+
+class Solution {
+public:
+    int subarraysDivByK(vector<int>& A, int K) {
+        unordered_map<int, int> count;
+        count[0] = 1;
+        int prefix = 0, result = 0;
+        for (const auto& a : A) {
+            prefix = (prefix + (a % K + K)) % K;
+            result += count[prefix]++;
+        }
+        return result;
+    }
+};