# 523 Continuous Subarray Sum

### Problem

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 the 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.
``````

Note: 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.

### Solutions

``````class Solution {
public boolean checkSubarraySum(int[] nums, int k) {
HashMap<Integer, Integer> remain = new HashMap<Integer, Integer>();
int sum = 0;
remain.put(0, -1);
for (int i = 0; i < nums.length; i ++) {
sum += nums[i];
if (k == 0) {
if (remain.containsKey(sum)) {
if (remain.get(sum) != i - 1 || i == 1) {
return true;
}
}
else {
remain.put(sum, i);
}
}
else {
int re = sum % k;
if (remain.containsKey(re)) {
if (remain.get(re) != i - 1) {
return true;
}
}
else {
remain.put(re, i);
}
}
}
return false;
}
}
``````