Java 求给定一组数的n个数的所有组合

我想写一个应用程序，找到给定数字集合中n个数字的所有可能组合，并返回它们的哈希集。。 例如，如果给定集合{1,5,7,9}和集合2的大小，则我将采用：

[1,5][1,7][1,9][5,7][5,9]

我有下面的代码，但是我不能每次修改给定大小的集合

import java.util.ArrayList;
import java.util.Arrays;

class SumSet {
    static void sum_up_recursive(ArrayList<Integer> numbers,ArrayList<Integer> partial) {

       System.out.println("sum("+Arrays.toString(partial.toArray())+")=");

       for(int i=0;i<numbers.size();i++) 
       {
           ArrayList<Integer> remaining = new ArrayList<Integer>();
             int n = numbers.get(i);
             for (int j=i+1; j<numbers.size();j++) 
                 remaining.add(numbers.get(j));

             ArrayList<Integer> partial_rec = new ArrayList<Integer>(partial);
             partial_rec.add(n);
             sum_up_recursive(remaining,partial_rec);
       }
    }
    static void sum_up(ArrayList<Integer> numbers) {
        sum_up_recursive(numbers,new ArrayList<Integer>());
    }
    public static void main(String args[]) {
        Integer[] numbers = {1,5,7,9};
        sum_up(new ArrayList<Integer>(Arrays.asList(numbers)));
    }
}

---

我们可以在SumSet.sum\u up\u recursiveArrayList、ArrayList、int方法中再添加一个参数sizeOfset，如下所示。请运行它告诉我它是否提供了您想要的输出

import java.util.ArrayList;
import java.util.Arrays;

public class SumSet {
    static void sum_up_recursive(ArrayList<Integer> numbers,
            ArrayList<Integer> partial , int sizeOfset) {

        if(partial.size() == sizeOfset)
        {
            System.out.println("sum(" + Arrays.toString(partial.toArray()) + ")=");
        }

        for (int i = 0; i < numbers.size(); i++) {
            ArrayList<Integer> remaining = new ArrayList<Integer>();
            int n = numbers.get(i);
            for (int j = i + 1; j < numbers.size(); j++)
                remaining.add(numbers.get(j));

            ArrayList<Integer> partial_rec = new ArrayList<Integer>(partial);
            partial_rec.add(n);
            sum_up_recursive(remaining, partial_rec, sizeOfset);
        }
    }

    static void sum_up(ArrayList<Integer> numbers) {
        sum_up_recursive(numbers, new ArrayList<Integer>(), 2);
    }

    public static void main(String args[]) {
        Integer[] numbers = { 1, 5, 7, 9 };
        sum_up(new ArrayList<Integer>(Arrays.asList(numbers)));
    }
}

---

我们可以在SumSet.sum\u up\u recursiveArrayList、ArrayList、int方法中再添加一个参数sizeOfset，如下所示。请运行它告诉我它是否提供了您想要的输出

import java.util.ArrayList;
import java.util.Arrays;

public class SumSet {
    static void sum_up_recursive(ArrayList<Integer> numbers,
            ArrayList<Integer> partial , int sizeOfset) {

        if(partial.size() == sizeOfset)
        {
            System.out.println("sum(" + Arrays.toString(partial.toArray()) + ")=");
        }

        for (int i = 0; i < numbers.size(); i++) {
            ArrayList<Integer> remaining = new ArrayList<Integer>();
            int n = numbers.get(i);
            for (int j = i + 1; j < numbers.size(); j++)
                remaining.add(numbers.get(j));

            ArrayList<Integer> partial_rec = new ArrayList<Integer>(partial);
            partial_rec.add(n);
            sum_up_recursive(remaining, partial_rec, sizeOfset);
        }
    }

    static void sum_up(ArrayList<Integer> numbers) {
        sum_up_recursive(numbers, new ArrayList<Integer>(), 2);
    }

    public static void main(String args[]) {
        Integer[] numbers = { 1, 5, 7, 9 };
        sum_up(new ArrayList<Integer>(Arrays.asList(numbers)));
    }
}

---

我将niiraj874u的答案中的递归方法更改为返回一个值。现在它给出了您想要的哈希集列表

static List<Set<Integer>> sum_up_recursive(List<Integer> numbers,
        Set<Integer> partial , int sizeOfset) {

    List<Set<Integer>> result = new ArrayList<Set<Integer>>();

    if(partial.size() == sizeOfset)
        result.add(partial);

    for (int i = 0; i < numbers.size(); i++) {
        ArrayList<Integer> remaining = new ArrayList<Integer>();
        int n = numbers.get(i);
        for (int j = i + 1; j < numbers.size(); j++)
            remaining.add(numbers.get(j));

        Set<Integer> partial_rec = new HashSet<Integer>(partial);
        partial_rec.add(n);
        result.addAll(sum_up_recursive(remaining, partial_rec, sizeOfset));
    }

    return result;
}

public static void main(String args[]) {
    Integer[] numbers = { 1, 5, 7, 9 };
    int size = 2;

    List<Set<Integer>> allCombinations = sum_up_recursive(Arrays.asList(numbers), new HashSet<Integer>(), size);

    for (Set<Integer> set : allCombinations) {
        for (Integer num : set)
            System.out.print(num + " ");
        System.out.println();
    }
}

---

我将niiraj874u的答案中的递归方法更改为返回一个值。现在它给出了您想要的哈希集列表

static List<Set<Integer>> sum_up_recursive(List<Integer> numbers,
        Set<Integer> partial , int sizeOfset) {

    List<Set<Integer>> result = new ArrayList<Set<Integer>>();

    if(partial.size() == sizeOfset)
        result.add(partial);

    for (int i = 0; i < numbers.size(); i++) {
        ArrayList<Integer> remaining = new ArrayList<Integer>();
        int n = numbers.get(i);
        for (int j = i + 1; j < numbers.size(); j++)
            remaining.add(numbers.get(j));

        Set<Integer> partial_rec = new HashSet<Integer>(partial);
        partial_rec.add(n);
        result.addAll(sum_up_recursive(remaining, partial_rec, sizeOfset));
    }

    return result;
}

public static void main(String args[]) {
    Integer[] numbers = { 1, 5, 7, 9 };
    int size = 2;

    List<Set<Integer>> allCombinations = sum_up_recursive(Arrays.asList(numbers), new HashSet<Integer>(), size);

    for (Set<Integer> set : allCombinations) {
        for (Integer num : set)
            System.out.print(num + " ");
        System.out.println();
    }
}

谢谢大家。。。 我也找到了这个解决方案

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;

public class Comb {

    static HashSet combine(Integer[] arr, int k, int startId, int[] branch, int numElem,HashSet arrSet)
    {
        if (numElem == k)
        {
            //System.out.println("k: "+k+(Arrays.toString(branch)));
            ArrayList<Integer> mySet = new ArrayList<Integer>();
            for(int i=0;i<branch.length;i++)
            {
                mySet.add(branch[i]);
            }
            arrSet.add(mySet);
            return arrSet;
        }

        for (int i = startId; i < arr.length; ++i)
        {
            branch[numElem++]=arr[i];
            combine(arr, k, ++startId, branch, numElem, arrSet);
            --numElem;
        }
        return arrSet;
    }

    public static void main(String args[]) 
    {
        int k = 3;
        Integer[] input ={1,5,7,9}; "ABCD".toCharArray(); 
        int[] branch = new int[k];//{0,0};//new char[k];
        HashSet arrSet=new HashSet();
        arrSet=combine(input, k, 0, branch, 0, arrSet);
    }
}

谢谢大家。。。 我也找到了这个解决方案

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;

public class Comb {

    static HashSet combine(Integer[] arr, int k, int startId, int[] branch, int numElem,HashSet arrSet)
    {
        if (numElem == k)
        {
            //System.out.println("k: "+k+(Arrays.toString(branch)));
            ArrayList<Integer> mySet = new ArrayList<Integer>();
            for(int i=0;i<branch.length;i++)
            {
                mySet.add(branch[i]);
            }
            arrSet.add(mySet);
            return arrSet;
        }

        for (int i = startId; i < arr.length; ++i)
        {
            branch[numElem++]=arr[i];
            combine(arr, k, ++startId, branch, numElem, arrSet);
            --numElem;
        }
        return arrSet;
    }

    public static void main(String args[]) 
    {
        int k = 3;
        Integer[] input ={1,5,7,9}; "ABCD".toCharArray(); 
        int[] branch = new int[k];//{0,0};//new char[k];
        HashSet arrSet=new HashSet();
        arrSet=combine(input, k, 0, branch, 0, arrSet);
    }
}

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它不适用于大于10的阵列！无论如何，thanksit不适用于大于10的阵列！无论如何，谢谢