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#523 - Continuous Subarray Sum

Medium • View on LeetCode • View on GitHub

Array Hash Table Math Prefix Sum

Problem 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.

Solution

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

  for (let i = 0, sum = 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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