523. Continuous Subarray Sum

Problem Link

Description

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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 <= nums[i] <= 109
• 0 <= sum(nums[i]) <= 231 - 1
• 1 <= k <= 231 - 1

Solution

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Python3

class Solution:
    def checkSubarraySum(self, nums: List[int], k: int) -> bool:
        N = len(nums)
 
        if N == 1: return False
        if k == 1: return True
        
        mp = {0 : -1}
        s = 0
 
        for i, x in enumerate(nums):
            s += x
            if s >= k: s %= k
 
            if s not in mp:
                mp[s] = i
            elif i - mp[s] >= 2:
                return True
            
        return False