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;
    }
}

Solution 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.

Solution 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);

Solution 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...