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.
Solution:
class Solution {
public boolean checkSubarraySum(int[] nums, int k) {
if (nums.length <= 1) return false;
for (int i = 1; i < nums.length; i ++) {
if (nums[i] == 0 && nums[i - 1] == 0) {
return true;
}
}
if (k == 0) return false;
k = Math.abs(k);
if (k == 1) return true;
Map<Integer, Integer> map = new HashMap();
int sum = nums[0];
map.put(0, -1);
map.put(sum, 0);
for (int i = 1; i < nums.length; i ++) {
sum += nums[i];
for (int j = 1; j * k <= sum; j ++) {
// sum - target = j * k
int target = sum - j * k;
if (map.containsKey(target) && (i - map.get(target)) > 1) {
return true;
}
}
map.putIfAbsent(sum, i);
}
return false;
}
}