Return the array elements arranged from outermost elements to the middle element, traveling clockwis-CodePudding

I'm trying to solve a task called Snail: given an n x n array, return the array elements arranged from outermost elements to the middle element, traveling clockwise - as you can see in the attached image.

I've already written the function but come across an error. Function works fine for while(result.length<=3) - it returns [1,2,3,4]. But for bigger numbers it shows an error -Uncaught TypeError: Cannot read properties of undefined (reading '2'). I've tried to rewrite the functions in a few different ways but keep seeing this error. I don't have any idea what could be the problem. The function down() is able to to return 4 but somehow it can't reach to 5 and beyond.

Thank you in advance for any help

function snail(array){
  let arr=[...array] //copy of a passed array
  let result=[] //here function will add next blocks
  const y=arr.length; const x=arr[0].length //this is to measure size to stop while
  let cY=0,cX=0;//current Y axis and current X axis
  /*For the purpose of this function both axes start as 0(top left corner) and when going down is  1 instead of -1 as normally in math*/

    
    while(result.length<=x*y){//this should go throw all of the blocks
    result.push(...arr[cY].splice(cX,1,null))//take block and replace it with null
    right()//search for a block - by default starts from right function
    }
    
    
    function right(){//goes right(next index of current array)
    if(arr[cY][cX 1])
    {cX =1}
    else{down()}
    }
    
    function down(){//goes down(next array of current index)
    if(arr[cY 1][cX])
    {cY  }
    else{left()}
    }
    
    function left(){//goes left(previous index of current array)
    if(arr[cY][cX-1])
    {cX--}
    else{up()}
    }
    
    function up(){//goes up(previous array of current index)
    if(arr[cY-1][cX])
    {cY--}
    else{right()}
    }
    
    return result
    }


console.log(snail([ [1,2,3],[8,9,4],[7,6,5]]))

CodePudding user response：

You are trying to access an array's element that doesn't exist :

arr[x   1][y]

You concidere this code will return false (undefined in fact) if indexes [x 1][y] doesn't exist

This is true only if arr[x 1] exist but, when arr[x 1] doesn't exist you also try to access the y'th element of this array which raises an error.

You should try something like this :

arr[x   1] && arr[x   1][y]

Which will return if first statement is false (undefined is interpreted as false) so it only check if [y] when [x 1] exists.

Using array method .at() :

arr.at(x   1).at(y) // (may) raise an error
arr.at(x   1)?.at(y) // return undefined instead

Hope it's clear enought ;)