Leetcode•Sep 08, 2025

Continuous Subarray Sum

Hazrat Ali

Leetcode

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

Solution
/**
 *
 * @param {number[]} nums
 * @param {number} k
 * @return {boolean}
 */
const checkSubarraySum = (nums, k) => {
  const map = new Map([[0, -1]]);

  let sum = 0;
  for (let i = 0; i < nums.length; i++) {
    sum += nums[i];

    if (k !== 0) {
      sum = sum % k;
    }

    if (map.has(sum)) {
      if (i - map.get(sum) >= 2) {
        return true;
      }
    } else {
      map.set(sum, i);
    }
  }

  return false;
};




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