# Question

Formatted question description: https://leetcode.ca/all/523.html

 523. Continuous Subarray Sum

Given a list of non-negative numbers and a target integer k, write a function to check
if the array has a continuous subarray of size at least 2 that sums up to a multiple of k,
that is, sums up to n*k where n is also an integer.

Example 1:

Input: [23, 2, 4, 6, 7],  k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.

Example 2:

Input: [23, 2, 6, 4, 7],  k=6
Output: True
Explanation: Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42.

Constraints:
The length of the array won't exceed 10,000.
You may assume the sum of all the numbers is in the range of a signed 32-bit integer.



# Algorithm

bruce force

note if k is 0 then mod will not work

# Code

Java

Java

class Solution {
public boolean checkSubarraySum(int[] nums, int k) {
int length = nums.length;
if (length < 2)
return false;
if (k == 0) {
for (int i = 1; i < length; i++) {
if (nums[i - 1] == 0 && nums[i] == 0)
return true;
}
return false;
}
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(0, -1);
int remainder = 0;
for (int i = 0; i < length; i++) {
remainder = (remainder + nums[i]) % k;
if (map.containsKey(remainder)) {
int prevIndex = map.get(remainder);
if (i - prevIndex > 1)
return true;
} else
map.put(remainder, i);
}
return false;
}
}