Create 0974-subarray-sums-divisible-by-k.java

Author: sujal-goswami

java/0974-subarray-sums-divisible-by-k.java

@@ -0,0 +1,17 @@
+class Solution {
+    public int subarraysDivByK(int[] nums, int k) {
+        int prefix_sum = 0;
+        int res = 0;
+        Map<Integer, Integer> map = new HashMap<>(); // remainder -> count
+        map.put(0, 1);
+
+        for(int n: nums){
+            prefix_sum += n;
+            int remainder = ((prefix_sum % k) + k) % k;  // twice modulo to avoid negative remainders
+
+            res += map.getOrDefault(remainder, 0);
+            map.put(remainder, map.getOrDefault(remainder, 0) + 1);
+        }
+        return res;
+    }
+}