[Medium] 1630. Arithmetic Subarrays

문제

https://leetcode.com/problems/arithmetic-subarrays/

Arithmetic Subarrays - LeetCode

A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. More formally, a sequence s is arithmetic if and only if s[i+1] - s[i] == s[1] - s[0] for all valid i.

수열은 적어도 두 개의 원소로 이루어져 있고, 두 개의 연속된 원소의 차이가 동일하다면 산술이라고 불린다. 더 공식적으로, 수열은 모든 유효한 i에 대해 s[i+1] - s[i] == s[1] - s[0]일 경우에만 산술이다.

 

예시

For example, these are arithmetic sequences:

1, 3, 5, 7, 9
7, 7, 7, 7
3, -1, -5, -9

The following sequence is not arithmetic:

1, 1, 2, 5, 7

You are given an array of n integers, nums, and two arrays of m integers each, l and r, representing the m range queries, where the ith query is the range [l[i], r[i]]. All the arrays are 0-indexed.

Return a list of boolean elements answer, where answer[i] is true if the subarray nums[l[i]], nums[l[i]+1], ... , nums[r[i]] can be rearranged to form an arithmetic sequence, and false otherwise.

 

Example 1:

Input: nums = [4,6,5,9,3,7], l = [0,0,2], r = [2,3,5]
Output: [true,false,true]
Explanation:
In the 0th query, the subarray is [4,6,5]. This can be rearranged as [6,5,4], which is an arithmetic sequence.
In the 1st query, the subarray is [4,6,5,9]. This cannot be rearranged as an arithmetic sequence.
In the 2nd query, the subarray is [5,9,3,7]. This can be rearranged as [3,5,7,9], which is an arithmetic sequence.

Example 2:

Input: nums = [-12,-9,-3,-12,-6,15,20,-25,-20,-15,-10], l = [0,1,6,4,8,7], r = [4,4,9,7,9,10]
Output: [false,true,false,false,true,true]

 

제약 조건

Constraints:

• n == nums.length
• m == l.length
• m == r.length
• 2 <= n <= 500
• 1 <= m <= 500
• 0 <= l[i] < r[i] < n
• -105 <= nums[i] <= 105

 

해결 과정

checkArithmetic 이라는 함수를 생성한다.

이 함수로 ar 배열의 차이가 일정한지 확인한다. 일정하면 true, 일정하지 않으면 false를 반환한다.

 

l과 r의 값을 기준으로 nums 배열을 slice 한다. slice한 배열을 내림차 순 정렬 후 checkArithmetic 함수를 통해 배열의 차이가 일정한지 값을 반환한다.

 

해결 코드

/**
 * @param {number[]} nums
 * @param {number[]} l
 * @param {number[]} r
 * @return {boolean[]}
 */
var checkArithmeticSubarrays = function(nums, l, r) {
    const checkArithmetic = ar => {
    const diff = ar[1] - ar[0];
    for(let i = 2; i < ar.length; i++)
      if(ar[i] - ar[i-1] != diff)
        return false;
    return true;
  }
  
  return l.map((_,i) => checkArithmetic(nums.slice(l[i], r[i]+1).sort((a,b) => a-b)) )
};