How to get lowest 3 elements in an int array

Question

Hi I want to get the lowest 3 elements of an array. By lowest I mean the minimum value. I cannot use the collections.Sort method as I need to know the index of the elements. Therefore I am using the following code to get the lowest, but I need to know how I can get the lowest 3.

int minimum = grades[1];
int index = 1;

for(i=1; i<= numberOfStudents; i++){
    if (grades[i]<minimum){
        minimum = grades[i];
        index = i;
    }
}

Simonnesimonpure

Why are you starting your array indexes at 1? – Rightful

There might be a better way, but I would just sort it by the value you want to and then just grab the first 3 of the sorted array. – Favata

@Jacob he specifically said he can't use that. – Mage

Just copy the array and sort the copy. Or keep track of 3 elements instead of 1 when looping through. Basic programming :p – Np

@Rightful - Because the first element is not relevant to what I need to achieve – Simonnesimonpure

@Keyser - How would I be able to keep track of 3 elements? – Simonnesimonpure

The top voted answer below has one way. I myself wouldn't have used an array though. The idea is the same as it is with 1 element, but you try to fit new values into any of the three (lowest, second-lowest,third-lowest). – Np

Java can be verbose in cases like this. In Scala for example this could be solved with a single line of code. val lowestThreeIndices = grades.zipWithIndex.sorted.take(3).map(_._2) – Lager

Answer 1

Here is a really simple way of doing it:

public static void main(String[] args) {
    int[] myArray = { 5, 8, 12, 9, 50, 11, 4 };

    System.out.println(Arrays.toString(myArray));
    System.out.println(Arrays.toString(getThreeLowest(myArray)));
}

private static int[] getThreeLowest(int[] array) {
    int[] lowestValues = new int[3];
    Arrays.fill(lowestValues, Integer.MAX_VALUE);

    for(int n : array) {
        if(n < lowestValues[2]) {
            lowestValues[2] = n;
            Arrays.sort(lowestValues);
        }
    }
    return lowestValues;
}

This outputs:

[5, 8, 12, 9, 50, 11, 4]
[4, 5, 8]

The call to Arrays.sort is only done to the local array, not your main array. The reason it does this is just to simplify the comparison against n.

Seismic

I need to know the indexes of the lowest 3 though – Simonnesimonpure

You could do exactly what he types, but instead of storing the values in the lowestValues array, store the index (you'd have to use a loop instead of a foreach), then add a comparator to the sort call that compares the values from the indexes stored in the lowestValues. – Audible

Answer 2

Building off what you had

    int[] grades = { 100, 99, 98, 97, 10, 95, 11, 9, 94 };
    int numberOfStudents = grades.length;

    int minimum = grades[1];
    int minimum2 = grades[1];
    int minimum3 = grades[1];
    int index = 1;
    int index2 = 1;
    int index3 = 1;

    for(int i=1; i< numberOfStudents; i++){
        if (grades[i]<minimum3 && grades[i]>=minimum2){
            minimum3 = grades[i];
            index3 = i;
        }
        if (grades[i]<minimum2 && grades[i]>=minimum){
            //We have a new 2nd lowest - shift previous 2nd lowest up
            minimum3 = minimum2;
            index3 = index2;
            minimum2 = grades[i];
            index2 = i;
        }
        if (grades[i]<minimum){
            //We have a new lowest - shift previous lowest up
            minimum3 = minimum2;
            index3 = index2;
            minimum2 = minimum;
            index2 = index;
            minimum = grades[i];
            index = i;
        }
    }
    System.out.println("Smallest is at " + index + " with value of " + minimum);
    System.out.println("Next Smallest is at " + index2 + " with value of " + minimum2);
    System.out.println("Next Smallest is at " + index3 + " with value of " + minimum3);

Demonolatry

Answer 3

This may be a bit 'too much' but off the top of my head possible that you could make an array of objects, each object containing the value and index it has in the original 'grades' array and sort that?

The only other way I can think of is to good through the array and manually keep track of the 3 lowest elements and their indexes like what you're already doing...

Macy

Answer 4

Take three variables: the smallest, second smallest and third smallest. In the same way you are finding your smallest element, find at each step which are the three smallest elements.

You need to check if any element is smaller than the smallest number, or it is between the smallest and the second smallest, or it is between the second smallest and the third smallest.

As this is probably an assignment, task or homework, i will not write the code here.

Albuminate

Lol thanks, its not an assignment. Im just helping out a friend – Simonnesimonpure

Answer 5

Can we do

    int[] myArray = { 5, 8, 12, 9, 50, 11, 4 };
    Arrays.sort(myArray);
    System.out.println(myArray[0] +","+ myArray[1] +","+ myArray[2]);

Prostitute

Are you asking? or answering? – Analysand