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So, recently I started a coding challenge to improve my coding skills. The context of the challenge is to find the right masses of a given List that sum up to a given weight of an animal. The function should return a List that includes all needed masses.

The given masses list includes the following elements: [1, 2, 4, 8, 16, 32, 64, 128]. The given weight is 145.

The code should also work for weights different to the given weight of 145.

Here is the code given by the challenge:

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;


class Scale {
    static List<Integer> getMasses(Integer weight, List<Integer> allMasses) {
        // You need to implement this method.
        // You can also add attributes to the class and add new methods or functions
        throw new NotImplementedException();
    }
}

Here is my current code:

class Scale {
    static List<Integer> getMasses(Integer weight, List<Integer> allMasses) {
        // You need to implement this method.
        // You can also add attributes to the class and add new methods or functions

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

        List<Integer> neededMasses = new ArrayList<Integer>();
           
           
        for(int i = 1; i < allMasses.size() + 1; i++){

            if(allMasses.get(allMasses.size() - i) == weight){
                neededMasses.add(allMasses.get(allMasses.size() - i));
                return neededMasses;
            }
            else if(allMasses.get(allMasses.size() - i) == 0){
                return neededMasses;
            }
            else if(allMasses.get(allMasses.size() - i) > weight){
                
                continue;
            }
            else{
                weight = weight - allMasses.get(allMasses.size() - i);
                neededMasses.add(allMasses.size() - i);
                
            }
        }

        throw new NotImplementedException();
    }
}

If I run my code now, the list that i should return includes [1, 4, 7]. But it should include [128, 16, 1].

Can someone help me to figure out how to get my code to work? Am I on the right track or is my code completly wrong?

Zardorin
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  • So, you've got powers of two weights, and you need to make a target weight? Why not just extract the set bits from the target. – Andy Turner Jul 29 '20 at 10:09
  • i would say that you should restart from 0, with another "way of thinking", if it's ok for you, i'll show you my solution on an answer – Alberto Sinigaglia Jul 29 '20 at 10:09
  • This answer might help https://stackoverflow.com/questions/3420937/algorithm-to-find-which-number-in-a-list-sum-up-to-a-certain-number – Marc Jul 29 '20 at 10:27
  • @AndyTurner I've got a target weight (in this example it is 145) and a list of masses. Out of this list I need to find a kombination of masses that sum up to the weight. – Zardorin Jul 29 '20 at 11:15
  • @Berto99 I would appreciate it if you'd show me your solution so i can get my head around this problem – Zardorin Jul 29 '20 at 11:16
  • @Zardorin yes. You can trivially test if you need to include, say, 16 by checking `target & 16 != 0`. This only works for weights which are powers of two, though. – Andy Turner Jul 29 '20 at 11:23
  • i think you should use some dynamic programming technique – Alberto Sinigaglia Jul 29 '20 at 13:03
  • @Berto99 Could you give me an example? I've never used such techniques and im struggeling to understand how to use them to solve my problem – Zardorin Jul 29 '20 at 21:26

0 Answers0