Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.
Example 1:
Input: nums = [1,1,1], k = 2
Output: 2
Example 2:
Input: nums = [1,2,3], k = 3
Output: 2
Constraints:
- 1 <= nums.length <= 2 * 104
- -1000 <= nums[i] <= 1000
- -107 <= k <= 107
class Solution {
public int subarraySum(int[] nums, int k) {
int sum = 0, result = 0;
Map<Integer, Integer> preSum = new HashMap<>();
preSum.put(0, 1);
for (int i = 0; i < nums.length; i++) {
sum += nums[i];
if (preSum.containsKey(sum - k)) {
result += preSum.get(sum - k);
}
preSum.put(sum, preSum.getOrDefault(sum, 0) + 1);
}
return result;
}
}