class Solution {
    public int subarraySum(int[] a, int k) {
        int n = a.length;
        int sumSoFar = 0;
        int result = 0;
        Map<Integer, Integer> sumFreq = new HashMap<>();
        sumFreq.put(0, 1);
        for(int i = 0; i< n; i++){
            sumSoFar += a[i];
            if(sumFreq.containsKey(sumSoFar - k)){
                result += sumFreq.get(sumSoFar - k);
            }
            int freq = sumFreq.getOrDefault(sumSoFar, 0) + 1;
            sumFreq.put(sumSoFar, freq);
        }
        return result;
    }
}