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Thread: A Challenge Coding problem! Java coding for combinational sum

  1. #1
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    Default A Challenge Coding problem! Java coding for combinational sum

    I got this java code for combinational sum:
    *****************************
    JavaScript:
    // Java program to find all combinations that
    // sum to a given value
    import java.io.*;
    import java.util.*;

    class GFG {

    static ArrayList<ArrayList<Integer> >
    combinationSum(ArrayList<Integer> arr, int sum)
    {
    ArrayList<ArrayList<Integer> > ans
    = new ArrayList<>();
    ArrayList<Integer> temp = new ArrayList<>();

    // first do hashing since hashset does not always
    // sort
    // removing the duplicates using HashSet and
    // Sorting the arrayList

    Set<Integer> set = new HashSet<>(arr);
    arr.clear();
    arr.addAll(set);
    Collections.sort(arr);

    findNumbers(ans, arr, sum, 0, temp);
    return ans;
    }

    static void
    findNumbers(ArrayList<ArrayList<Integer> > ans,
    ArrayList<Integer> arr, int sum, int index,
    ArrayList<Integer> temp)
    {

    if (sum == 0) {

    // Adding deep copy of list to ans

    ans.add(new ArrayList<>(temp));
    return;
    }

    for (int i = index; i < arr.size(); i++) {

    // checking that sum does not become negative

    if ((sum - arr.get(i)) >= 0) {

    // adding element which can contribute to
    // sum

    temp.add(arr.get(i));

    findNumbers(ans, arr, sum - arr.get(i), i,
    temp);

    // removing element from list (backtracking)
    temp.remove(arr.get(i));
    }
    }
    }

    // Driver Code

    public static void main(String[] args)
    {
    ArrayList<Integer> arr = new ArrayList<>();

    arr.add(900);
    arr.add(800);
    arr.add(700);
    arr.add(600);
    arr.add(500);
    arr.add(100);
    arr.add(50);
    arr.add(1);
    int sum = 2000;

    ArrayList<ArrayList<Integer> > ans
    = combinationSum(arr, sum);

    // If result is empty, then
    if (ans.size() == 0) {
    System.out.println("Empty");
    return;
    }

    // print all combinations stored in ans

    for (int i = 0; i < ans.size(); i++) {

    System.out.print("(");
    for (int j = 0; j < ans.get(i).size(); j++) {
    System.out.print(ans.get(i).get(j) + " ");
    }
    System.out.print(") ");
    }
    }
    }
    **************************************
    what if I have large numbers like 900, 800, 700, 600, 500, 90, 80, 70, 60, 50, 9, 8, 7, 6, 5, 4, 3, 2, 1. and I want the combination of numbers to sum to 2000, how man listed combination. There would be many ones to list, how to limit the pick of 1s or 2s elements if it is going to be too many to list?

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: A Challenge Coding problem! Java coding for combinational sum

    Please edit your post and wrap your code with code tags:

    [code]
    **YOUR CODE GOES HERE**
    [/code]

    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

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