I'm currently still learning the basic JS and wondering how to answer this array type of question.

Question

//Given the participants' score sheet for your University Sports Day, you are required to find the runner-up score. You are given N scores. Store them in a list and find the score of the runner-up.

//Input Format

//The first line contains N. The second line contains an array A[] of N integers each separated by a space.

//Output Format

//Print the runner-up score.

//Sample Input: [5,2,3,6,6,5]
//Sample Output: 5

This is my code

function uniqueScore (value, index, self) {
   return self.indexOf(value) === index
}
var score = [5,2,3,6,6,5]
var filter = score.filter(uniqueScore)
var descSort = filter.sort().reverse()

function runnerUpScore(x) {
    var runnerUp = descSort
    return runnerUp
}
console.log(runnerUpScore(x))

The condition is i'm stuck when already sorting the array and removing duplicate. Hence, I need some guidance how to call the sorted array and only showing the index 1 from array list to show the runner up score.

CodePudding user response：

The problem with your approach is you are sorting the array and then reversing it which costs lots of computation. Here is a simple solution in O(n). It iterates the array only once and finds the second-largest score, which is the runner-up score.

var scores = [1,2,3,4,5];

const runnerUpScore = (scores) => {
  scores = [... new Set(scores)] // get unique elements
  var largest = -1;
  var secondLargest = -1;
  
  scores.forEach((score) => {
    if(score >= largest) {
      secondLargest = largest;
      largest = score;
    } else if (score > secondLargest) {
      secondLargest = score;
    }
  });
  
  return secondLargest;
}

console.log(runnerUpScore(scores));

CodePudding user response：

1. .sort() reverse:

   let scores = [5, 2, 3, 6, 6, 5];
   let reverseOrder = scores.sort((a, b) => b - a);
   // [6, 6, 5, 5, 3, 2]
   

2. Filter out duplicates by converting array into a Set() then back to an array:

   let set = new Set(reverseOrder)
   // {6:6, 5:5, 3:3, 2:2} this is a representation there's much more to a Set.
   let unique = [...set]
   // [6, 5, 3, 2]
   

3. Get the score in the second index position:

   unique[1]
   // 5
   

const scores = [5, 2, 3, 6, 6, 5];

const reverseOrderUnique = [...new Set(scores.sort((a, b) => b - a))];

console.log(reverseOrderUnique);
console.log('Runner Up: ' reverseOrderUnique[1]);