Java 8 need help with a program!

[dronikal]

Hello!I have ArrayList full of random Integers between 0-1000.And i need to get the index of the element with the highest value under 800 and the 10 highest values under 800.And I have to do that without sorting the list.

All I have until now what i could make by myself is this:

public static void main(String[] args) {
        ArrayList<Integer> list=new ArrayList<>(); 
        Random gen=new Random();                                                                
        for (int i = 0; i <100; i++) {
            int counter=gen.nextInt(1000);                                
            list.add(counter);                        
        }
        int maxindex=0;    
        for (int i = 1; i <list.size(); i++) {
            int number1=list.get(maxindex);
            int number2=list.get(i);
            if (number1<800) {
                if(number2<800){
                    if(number2>number1){
                         maxindex=i;
                    }    
                }
            }
            else {
                if(number2<800){
                    maxindex=i;
                }
            }
        }
    }

[Guest]

Are you allowed to sort your 10 maximum values? If so, there is an easy way to maintain a sorted data structure. I will so no more in the interests of not giving away a possible solution.

[dronikal]

No sorting at all.I know the collection.sort easy way but I'm not allowed to use it.

[fletch to 99]

You could just push all of the indexes you find to a stack with a maximum size of 10. 

[Guest]

5 minutes ago, dronikal said:

No sorting at all.I know the collection.sort easy way but I'm not allowed to use it.

Are you allowed to use a TreeMap?

[dronikal]

11 minutes ago, SSL said:

Are you allowed to use a TreeMap?

I'm afraid I'm too new to java 8 to know what that is;)

[dronikal]

The idea behind the program is that every random number is the length of a gene so i need to find the position of the 10 longest genes under 800 bases.So any sorting will result in me losing the position of the gene in the chromosome.

[jslowik]

Off the top of my head I'd think using a tree map, the position could be used as the key value. Sort by the random number. It'd be out of order, but the key value would keep track of the order they were in.

[Guest]

1 hour ago, dronikal said:

I'm afraid I'm too new to java 8 to know what that is;)

Then look it up in the Java docs. It sounds like exactly what you need. As the comment above describes, use the random number as the key and the position in your list the value. When the number of elements in your TreeMap exceeds 10, just kick out the element with the smallest key (the first in the tree). I also recommend that you read about Minimum Heaps and eventually Red-Black trees, which are the implementation used for Java TreeMaps.