Basic Algorithm

JavaScript
#1

I’ve been working on this algorithm for almost a day and cant get it to work. It’s the ‘return largest number in arrays’. Please help.


function largestOfFour(arr) {
  // You can do this!
  let arrAnswer = [];
  let largestNum = 0;
  for(let i = 0; i <= arr.length; i++){
      arrAnswer = arr[i];
    for(let j = 0; j <= arr[i].length; j++){
      if(arr[i][j] > largestNum){
      largestNum = arr[i][j]; 
      }
    }
    }
  
  return largestNum;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
#2

You are getting the ​"TypeError: Cannot read property ‘length’ of undefined" message, because you are trying to reference an element in arr (arr[4]) which does not exist. The reference to arr[4] is undefined, so when you attempt to get the length of arr[4] in the inner for loop condition (shown below), you get the message because undefined does not have a length property.

for(let j = 0; j <= arr[i].length; j++){

Why are you even referencing a non-existent element? Because you have accidentally forgotten that arrays are zero-indexed, so the highest index for an array with 4 elements will be 3. The problem is your outer for loop condition (shown below), uses <= instead of <, which allows i to go to 4.

for(let i = 0; i <= arr.length; i++){

Fixing both of the for loop conditions will not completely solve the challenge for you, but will fix the errors causing your code to hault.

#3

Yes. errors are gone. I’m only getting the largest of the last sub-array though.

#4

That is because as you get the largestNum for each sub array, you need to be building a final array which will hold each largestNum, so you can return the final array at the end, instead of just the largest largestNum overall.

HINT: After the inner for loop completes each time, largestNum will be the largest number for the sub array (arr[i]) which was just iterated.

#5

Got it. Thx for the help.

#6

Thought I had it done. The algorithm works fine on the browser console but doesn’t pass fcc tests. If someone can tell me why, that would be great.


function largestOfFour(arr) {
  // You can do this!
  let arrAnswer = [];
  for(let i = 0; i < arr.length; i++){
      let largestNum = 0;
    for(let j = 0; j < arr[i].length; j++){
      if(arr[i][j] > largestNum){
      largestNum = arr[i][j]; 
      }
    }
    arrAnswer[i] = largestNum;
    }
   
  return arrAnswer;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
#7

newer mind. fixed it

#8