第二大数组

Question

I am just trying to do this easy thing(make an array of numbers and then get the second biggest number of the same array) and I can't understand why it does not push chosen numbers from one array to the second one(from which it should print out the second biggest number).

 var cisla = []; var i = 0; for(var i=0; i<5; i++){ var x = prompt("Put " + (i+1) + ". number"); cisla[i] = x; } var p = document.createElement("p"); p.innerHTML = "Your array: " + cisla; document.getElementsByTagName("body")[0].appendChild(p); var najvacsie; var index; var cisla2 = []; var dlzka = cisla.length; while(i<dlzka){ najvacsie = cisla[0]; for(var x=0; x<cisla.length; x++){ if(najvacsie < cisla[x]){ najvacsie = cisla[x]; index = cisla.indexOf(najvacsie); } } cisla2.push(najvacsie); cisla.splice(index, 1); i++; } var pp = document.createElement("p"); pp.innerHTML = "Ordered array: " +cisla2; document.getElementsByTagName("body")[0].appendChild(pp); var ppp = document.createElement("p"); ppp.innerHTML = "The 2nd biggest number of your array is: " + cisla2[1]; document.getElementsByTagName("body")[0].appendChild(ppp); 

Thank you for your answers.

Answer 1

I made some changes, see comments.

But just to show you the main problem in your code:

if (najvacsie < cisla[x]){
    najvacsie = cisla[x];
    index = cisla.indexOf(najvacsie);
}

The problem is, if your najvacsie has already the biggest value, than the index is never set, so the next

cisla.splice(index, 1);

is either spliced with the last value, or if undefined it takes 0 as value for splicing (which could be expected behavior in the first round).

Now here is the working model:

 var array = []; for (var i = 0; i < 5; i++) { var x = prompt("Put " + (i + 1) + ". number"); array[i] = parseInt(x, 10); // otherwise it will sorted by string } var p = document.createElement("p"); p.innerHTML = "Your array: " + array; document.getElementsByTagName("body")[0].appendChild(p); var tempValue; var index; var orderedArray = []; while (array.length) { // that is shorter tempValue = array[0]; for (var x = 0; x < array.length; x++) { if (tempValue < array[x]) { tempValue = array[x]; } } index = array.indexOf(tempValue); // move this here orderedArray.push(tempValue); array.splice(index, 1); } //orderedArray = array.slice(0).sort().reverse(); // that may be better ... var pp = document.createElement("p"); pp.innerHTML = "Ordered array: " + orderedArray; document.getElementsByTagName("body")[0].appendChild(pp); var ppp = document.createElement("p"); ppp.innerHTML = "The 2nd biggest number of your array is: " + orderedArray[1]; document.getElementsByTagName("body")[0].appendChild(ppp); 

Answer 2

You can do it in linear time (I'll try to come up with a generic way to do it later)

function secondBiggestOf(array) {
    var biggest = -Infinity;
    var secondBiggest = -Infinity;

    for (var i = 0, l = array.length; i < l; i++) {
       var current = array[i];

       if (biggest < current) {
           var tmp = biggest;
           biggest = array[i];

           if (secondBiggest !== -Infinity) {
               secondBiggest = tmp;
           }
       } else if (secondBiggest < current) {
           secondBiggest = current;
       }
    }
    return secondBiggest;
}