Given an integer array nums and an integer k, return true if nums has a good subarray or false otherwise.
A good subarray is a subarray where:
its length is at least two, and
the sum of the elements of the subarray is a multiple of k.
Note that:
A subarray is a contiguous part of the array.
An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k.
Example 1:
Input: nums = 23,2,4,6,7, k = 6
Output: true
Explanation: 2, 4 is a continuous subarray of size 2 whose elements sum up to 6.
Example 2:
Input: nums = 23,2,6,4,7, k = 6
Output: true
Explanation: 23, 2, 6, 4, 7 is an continuous subarray of size 5 whose elements sum up to 42.
42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer.
Example 3:
Input: nums = 23,2,6,4,7, k = 13
Output: false
Constraints:
1 <= nums.length <= 105
0 <= numsi <= 109
0 <= sum(numsi) <= 231 - 1
1 <= k <= 231 - 1
It's easy to come up with prefix array, but the potential bug is that the its length is at least two. The following code is finished after several attempts:
python
class Solution:
def checkSubarraySum(self, nums: List[int], k: int) -> bool:
l = len(nums)
if (l <= 1):
return False
prefix_dic = {0:-1} # take care 0 is with any prefix
cur_sum = 0
for i in range(l):
cur_sum = (cur_sum+nums[i]) % k
# take care the following conditions
if cur_sum in prefix_dic and (i-prefix_dic[cur_sum] >= 2):
return True
if cur_sum not in prefix_dic:
prefix_dic[cur_sum] = i
return False