Add BinarySubarrayWithSumGoal class with hashmap approach

Author: harshithasudhakar

HashMap/Sliding Window/BinarySubarrayWithSumGoal.java

@@ -0,0 +1,26 @@
+class BinarySubarrayWithSumGoal { //Hashmap approach
+    public int numSubarraysWithSum(int[] nums, int goal) {
+        int n = nums.length;
+        int[] prefixSum = new int[n];
+
+        prefixSum[0] = nums[0];
+        for(int i = 1; i<n; i++){
+            prefixSum[i] = prefixSum[i-1] + nums[i];
+        }
+
+        int count = 0;
+
+        Map<Integer, Integer> map = new HashMap<>();
+        map.put(0, 1);
+
+        for(int i = 0; i<n; i++){
+            int remaining = prefixSum[i] - goal;
+            if(map.containsKey(remaining)){
+                count += map.get(remaining);
+            }
+            map.put(prefixSum[i], map.getOrDefault(prefixSum[i], 0) + 1);
+        }
+
+        return count;
+    }
+}