How to capture two large integers from a Javascript array and return the value to the DOM?

Question

I wrote a solution to take a list of integers entered through a form. It works. It gives you the sum of the two largest integers and sends them to the DOM. However, it is not very efficient for large arrays, for example, 1 million integers.

How can I improve this solution to be more effective.

App.js

// This function reverses the order of the array and places the biggest numbers first function sortNumber(a, b) { return b - a; } // this function is used to ensure the user didn't enter any letters function getArray() { var alphaExp = /^[a-zA-Z]+$/; // This function takes the array, orders it, adds the sum of the two largest numbers and returns the value function sumOf(x) { // Sort the ary with the sortNumber function array.sort(sortNumber); // Then we add the two biggest numbers of the array and save it to the result variable. var result = array[0] + array[1]; // Then we share the result with the user by updating the browser var myHeading = document.querySelector('h2'); myHeading.textContent = "The sum of your two biggest numbers is: " + result; // Like a good student, it important to show your work var showYourWork = document.querySelector('h3'); showYourWork.textContent = array[0] + " + " + array[1] + " = " + result; } // This grabs the value of the input var arrayField = document.getElementById('arrayField').value; if (arrayField.match(alphaExp)) { // Fail if user enters letters var raiseError = document.querySelector('h5'); raiseError.textContent = 'No not letters! We want numbers!!'; } else { var array = JSON.parse("[" + arrayField + "]"); if (arrayField.length < 2) { // If the user enters only 1 number, tell them to enter more! var raiseError = document.querySelector('h5'); raiseError.textContent = 'Please enter atleast two numbers seperated by commas for us to add!' } else { // When the user enters a list of numbers, run the sumOf function. sumOf(arrayField); //Make the error go away var raiseError = document.querySelector('h5'); raiseError.textContent = ''; } } }; // use an eventlistener for the event (This is where the magic happens) var subButton = document.getElementById('subButton'); subButton.addEventListener('click', getArray, false); 

Answer 1

You don't need to sort it, just search linearly for the two largest:

EDIT: The code below should work asymptotically faster than the OP code. First, the OP performs sorting, which can be done in O (n log n), assuming a random list. My code does a linear list search in O(cn) using c = 2 (two loops are optional but simple). The solution for ceil(n log n) = 2n with n positive integer is 14, that is, for each list longer than 14 entries, the code below is faster. For example: per million records, the ratio is 13,815,511 to 2,000,000, which is more than six times faster. You can do the same in a single loop that shortens the execution time (theoretically, but it is also slightly faster due to better locality).

 function maxtwo_wrong(a){ var b1 = -Infinity; var b2 = -Infinity; for (var i=0; i < a.length; i++) { if (a[i] > b1) { b1 = a[i]; } } for (var i=0; i < a.length; i++) { if (a[i] > b2 && a[i] < b1) { b2 = a[i]; } } return [b1,b2]; } 

EDIT-2: the code above maxtwo_wrong does not seem to meet the requirements, so I wrote another maxtwo_right and put it below. Please OP, tell me which one meets your requirements so that I can remove the wrong one.

EDIT-3: simplified and fixed.

 function maxtwo_right(a){ var b1 = -Infinity; var b2 = -Infinity; for (var i=0; i < a.length; i++) { // If the current entry is bigger than variable b1 // keep the old value in the variable b2 and set b1 to the // value of the current entry if (a[i] > b1) { b2 = b1; b1 = a[i]; } // if the current entry equals b1 set the variable b2 to // the value of the current entry else if(a[i] === b1){ b2 = a[i]; } } // return the sum of the two variables as requested return b1 + b2; } 

Answer 2

Finally, I took the time to sit down and work on it. I was looking for a problem all the time.

Here is my new solution

 // This function adds the sum of the two largest integers of an array and returns the value function topTwoInt(theArray) { var intArray = theArray; var highestInt = -Infinity; var secondHighestInt = -Infinity; var answer = 0; //Loop through the array for (var i=0; i < intArray.length; i++) { //grab the biggest int and assign it to the highestInt variable; if (intArray[i] > highestInt) { secondHighestInt = highestInt; highestInt = intArray[i]; } //If the next number is equal too highestInt or greater than secondHighestInt //Make that number become the new secondHighestInt else if(intArray[i] === highestInt || intArray[i] > secondHighestInt) { secondHighestInt = intArray[i]; } } answer = highestInt + secondHighestInt; return answer; }; 

This decision is largely inspired by @deamentiaemundi Thank you man.