Leetcode diary: 1630 - Arithmetic Subarrays

This is a new series where I document my struggles of leetcode questions hoping seeing however small of an audience I get gives me the motivation to continue.

Today's question

This was an okay question. After getting over the beginning confusion over the parameters, I noticed a trend is that the steps should be the same if a given arithmetic sequence is sorted. This is just an intuition, it's not something I can justify fully, hopefully in the interviews the interviewer is okay with just the observation.

I then wrote out my process as below:

so we want an answerArray = [];
it will contain the list of booleans for final return
then we loop on l & r
get the range of numbers via: nums.slice(l, r);
we then put the numbers into isArith function
said function will sort(?) the array
and determine the difference between each step
finally return the result and append to answerArray

I tried my initial code, this passed the given test case:

var checkArithmeticSubarrays = function(nums, l, r) {    

    const answerArray = [];

    l.forEach(function(lindex, index){
        answerArray.push(
            isArithSimpleSort(nums.slice(lindex, r[index]+1))
        );
    });

    return answerArray;
};

function isArithSimpleSort(nums) {
    if (nums.length <= 2) { return true } 

    nums = nums.sort();

    const step = Math.abs(nums[0] - nums[1]);

    for (let i=2; i < nums.length; i++) {
        if(step != Math.abs(nums[i] - nums[i-1])) {
            return false;
        }
    }

    return true;
}

However I failed the submission. As I looked at the failed test case, I realized perhaps I need to do sorting over absolute values and the default; whichever returns true, I'll record.

This quick modification worked, but it had terrible performance, so I found a solution in the discussion with good performance:

const checkArithmeticSubarraysa = (nums, l, r) => {

  const chechArithmetic = 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) => chechArithmetic(nums.slice(l[i], r[i]+1).sort((a,b) => a-b)) )
};

After reading this crazy code in detail, it's always hard to read others' code, I realize our code is basically the same. As I compared, I realized that the sort function is just a-b instead of absolute values or plain sort function. I then tried just the absolute function sort and see if I can pass the submission. It did. I was confused for a minute, then I realized that javascript sort function on ints are string based, not ints. After realizing my newbie mistake I quickly modified my code and got this final solution faster than at least 21%: (this solution is the same as the fastest, guess i am just unlucky that the server is busier or something :P)

var checkArithmeticSubarrays = function(nums, l, r) {    
    const answerArray = []
    l.forEach(function(lindex, index){
        answerArray.push(
            isArithAbsSort(nums.slice(lindex, r[index]+1))
        );
    });

    return answerArray;
};

function isArithAbsSort(nums) {
    if (nums.length <= 2) { return true } 

    nums = nums.sort(function(a,b){
        return a > b ? 1 : -1
    });

    const step = Math.abs(nums[0] - nums[1]);

    for (let i=2; i < nums.length; i++) {
        if(step != Math.abs(nums[i] - nums[i-1])) {
            return false;
        }
    }

    return true;
}

Let me know anything on your mind after reading through this, THANKS!