Given an unsorted array of integers, find the number of continuous subarrays having sum exactly equal to a given number k.
Examples:
Input: arr = [10, 2, -2, -20, 10], k = -10 Output: 3 Explaination: Subarrays: arr[0...3], arr[1...4], arr[3...4] have sum exactly equal to -10.
Input: arr = [9, 4, 20, 3, 10, 5], k = 33 Output: 2 Explaination: Subarrays: arr[0...2], arr[2...4] have sum exactly equal to 33.
Input: arr = [1, 3, 5], k = 0
Output: 0 Explaination: No subarray with 0 sum.
Constraints:
- 1 ≤ arr.size() ≤ 105
- -103 ≤ arr[i] ≤ 103
- -107 ≤ k ≤ 107