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I am working on an assignment. I have the basics down of what I need done, but for some reason, the compareTo is not sorting properly on one set of example inputs. The first set of inputs sorts properly and returns the right value, but the second set rearranges, but does not sort. Basically I have an object Cow, that has a time and a number of flowers eaten. I want to take these objects and sort them, first by time, shortest time first, and then by flowers eaten, largest amount first. So if I had 3 cows, 1 and 10, 2 and 5, 2 and 7. I would sort them, first, third and second. Hopefully that makes sense. I am not sure why the Collection.sort is not working as intended...but hopefully someone can lead me in the right direction of what I am doing wrong.

Here is my code so far:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Flowers {

    public static void main(String[] args) {
        ArrayList<Cow> list = new ArrayList<Cow>();
        Scanner input = new Scanner(System.in);
        final int numOfCows = Integer.parseInt(input.next());
        int totalFlowers = 0;

        // Fills the list with the cows attributes (time and flowers destroyed)
        for (int i = 0; i < numOfCows; i++) {
            int theTime = Integer.parseInt(input.next());
            int theFlowers = Integer.parseInt(input.next());
            final Cow theCow = new Cow(theTime, theFlowers);
            list.add(theCow);
        }

        Collections.sort(list);

        for (int i = 0; i < list.size(); i++) {
            for (int k = 0; k < list.get(i).time; k++)
                for (int j = i + 1; j < list.size(); j++) {
                    totalFlowers += (list.get(j).flowers * 2);
                }
        }

        System.out.println(totalFlowers);

        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }

        input.close();
    }

    public static final class Cow implements Comparable<Cow> {
        public final int time;
        public final int flowers;

        public Cow(final int theTime, final int theFlowers) {
            time = theTime;
            flowers = theFlowers;
        }

        @Override
        public int compareTo(Cow other) {
            int compared = 1;
            if (this.time < other.time) {
                compared = -1;
            } else {
                if (this.flowers > other.flowers) {
                    compared = -1;
                }
            }
            return compared;
        }

        @Override
        public String toString() {
            return String.format("Time:%d Flowers: %d", time, flowers);
        }
    }
}
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3 Answers 3

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In the statement if (this.flowers > other.flowers) you do not consider the fact that this.time could still be greater than other.time.

You do also not consider the case when time and flowers are equal to those of the other Cow.

I'd prefer doing something like this:

public int compareTo(Cow other) {
    int compare = this.time - other.time;
    if(compare == 0) {
        compare = other.flower - this.flower;
    }
    return compare;
}
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6 Comments

Everything is sorting, but I am still getting a strange number from the code. I use the input 13 82 77 97 49 73 77 60 100 94 24 31 74 5 76 24 41 100 70 97 89 38 68 41 93 89 16 and should get an output of 362670. Basically, there is a farmer who is transporting cows. The time is how long it takes him to get the cow into the barn....and then the same time to get back to the cows...and while he does it, the cows are eating flowers. So this is supposed to show how many flowers are eaten up until all cows are in their barns. The list is sorting properly now, but I am getting 424074.
@user2317377 Why are you using three nested for-loops? If you just want the sum of the flowers variables, use one loop.
Well...it isn't just the sum of the flowers. The farmer is bringing a cow back to the barn, so the cows are eating the flowers/minute to the barn and back from the barn...and then he brings the 2nd cow, and they keep eating. So basically, I have to account for all of the cows, all of the minutes of traveling, and then rest of the cows and how much they are eating during this traveling. Am I wrong?
@user2317377 Then 424074 should be the right answer, unless you've read the assignment wrong, or the input is wrong. By the way, it's possible with two for-loops if you multiply get(i).time with get(j).flowers.
Well let me try and explain it better. Maybe I am not doing a good job. There are cows eating flowers, the farmer is moving them, one at a time to their barns to stop them from eating flowers. While he moves a cow, the remaining cows eat flowers/minute for the trip to the barn, and the trip back. Then he takes the second cow, and the rest keep eating, and so on and so on.
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Essentially, you want to compare flower count only if time count is same. 

    public int compareTo(Cow other) {
        int comparison = new Integer(this.time).compareTo(new Integer(other.time));
        if (comparison == 0) {
            return (-1) * new Integer(this.flowers).compareTo(new Integer(other.flowers));
        } 
        return comparison;
    }
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3 Comments

If I use input of: 6 3 1 2 5 2 3 3 2 4 1 1 6... it puts 2 3 before 2 5. It should be the other way around...
the result of that input should be 86 from this code. And if I use 13 82 77 97 49 73 77 60 100 94 24 31 74 5 76 24 41 100 70 97 89 38 68 41 93 89 16...the result should be 362670. Basically, there is a farmer who is transporting cows. The time is how long it takes him to get the cow into the barn....and then the same time to get back to the cows...and while he does it, the cows are eating flowers. So this is supposed to show how many flowers are eaten up until all cows are in their barns.
The inner comparison should be descending, had missed that out. The comparison value is multiplied by (-1).
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//Here is sorted List alphabetically with syncronized
//Here is sorted List alphabetically with syncronized
package com.mnas.technology.automation.utility;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

import org.apache.log4j.Logger;
/**
* 
* @author manoj.kumar
*/
public class SynchronizedArrayList {
static Logger log = Logger.getLogger(SynchronizedArrayList.class.getName());
@SuppressWarnings("unchecked")
public static void main(String[] args) {

List<Employee> synchronizedList = Collections.synchronizedList(new ArrayList<Employee>());
synchronizedList.add(new Employee("Aditya"));
synchronizedList.add(new Employee("Siddharth"));
synchronizedList.add(new Employee("Manoj"));
Collections.sort(synchronizedList, new Comparator() {
public int compare(Object synchronizedListOne, Object synchronizedListTwo) {
//use instanceof to verify the references are indeed of the type in question
return ((Employee)synchronizedListOne).name
.compareTo(((Employee)synchronizedListTwo).name);
}
}); 
/*for( Employee sd : synchronizedList) {
log.info("Sorted Synchronized Array List..."+sd.name);
}*/

// when iterating over a synchronized list, we need to synchronize access to the synchronized list
synchronized (synchronizedList) {
Iterator<Employee> iterator = synchronizedList.iterator();
while (iterator.hasNext()) {
log.info("Sorted Synchronized Array List Items: " + iterator.next().name);
}
}

}
}
class Employee {
String name;
Employee (String name) {
this.name = name;

}
}
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