public class Solution {

/*public int subarraySum(int[] nums, int k) {

int count = 0;

for (int start = 0; start < nums.length; start++) {

int sum = 0;

for (int end = start; end < nums.length; end++) {

sum += nums[end];

if (sum == k)

count++;

}

}

return count;

}*/

public int subarraySum(int[] nums, int k) {

int count = 0, sum = 0;

HashMap < Integer, Integer > map = new HashMap < > ();

map.put(0, 1);

for (int i = 0; i < nums.length; i++) {

sum += nums[i];

// check if sum - k in hash

if (map.containsKey(sum - k))

count += map.get(sum - k);

// push sum into hash

map.put(sum, map.getOrDefault(sum, 0) + 1);

}

return count;

}

}