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523. Continuous Subarray Sum

Description

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

Solutions

• Java
• C++
• Python
• Go

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

• class Solution {
  public:
      bool checkSubarraySum(vector<int>& nums, int k) {
          unordered_map<int, int> mp;
          mp[0] = -1;
          int s = 0;
          for (int i = 0; i < nums.size(); ++i) {
              s += nums[i];
              int r = s % k;
              if (mp.count(r) && i - mp[r] >= 2) return true;
              if (!mp.count(r)) mp[r] = i;
          }
          return false;
      }
  };
  

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

• func checkSubarraySum(nums []int, k int) bool {
  	mp := map[int]int{0: -1}
  	s := 0
  	for i, v := range nums {
  		s += v
  		r := s % k
  		if j, ok := mp[r]; ok && i-j >= 2 {
  			return true
  		}
  		if _, ok := mp[r]; !ok {
  			mp[r] = i
  		}
  	}
  	return false
  }
  

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