560-Subarray-Sum-Equals-K.java

class Solution {

    public int subarraySum(int[] nums, int k) {
        int res = 0, sum = 0;
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(0, 1);
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            int diff = sum - k;
            if (map.containsKey(diff)) {
                res += map.get(diff);
            }
            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        return res;
    }
}