给定数组a[1,2,3],用a里面的元素来生成一个长度为5的数组，打印出其排列组合

给定数组a[1,2,3],用a里面的元素来生成一个长度为5的数组，打印出其排列组合

ruby代码：

def all_possible_arr arr, length = 5

    ret = []

    length.times do

        if ret.empty?

            ret = arr.map {|i| [i]}

        else

            new_ret = []

            ret.each do |r|

                arr.each do |e|

                    new_ret << r.clone.unshift(e)

                end

            end

            ret = new_ret

        end

    end

    ret

end

p all_possible_arr [1, 2, 3] 

JAVA代码：

package com.test;

import java.util.ArrayList;

public class TestEmu {

    @SuppressWarnings("unchecked")

    public ArrayList<ArrayList<Integer>> getArray(ArrayList<Integer> ll, int len) {

        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();

        for (int i = 0; i < len; i++) {

            if (list.size() == 0) {

                for (int j = 0; j < ll.size(); j++) {

                    ArrayList<Integer> temp = new ArrayList<Integer>();

                    temp.add(ll.get(j));

                    list.add(temp);

                }

            } else {

                ArrayList<ArrayList<Integer>> temp = new ArrayList<ArrayList<Integer>>();

                for (ArrayList<Integer> l : list) {

                    for (int m : ll) {

                        ArrayList<Integer> t = (ArrayList<Integer>) l.clone();

                        t.add(m);

                        temp.add(t);

                    }

                }

                list = temp;

            }

        }

        return list;

    }

    public static void main(String[] args) {

        ArrayList<Integer> list = new ArrayList<Integer>();

        list.add(1);

        list.add(2);

        list.add(3);

        TestEmu te = new TestEmu();

        ArrayList<ArrayList<Integer>> ll = te.getArray(list, 5);

        for(ArrayList<Integer> l:ll){

            for(int i:l){

                System.out.print(i+" ");

            }

            System.out.println();

        }

    }

}

递归实现：

package com.test.util;

import java.util.Arrays;

public class Test {

	private int end;

	private int[] arr;

	public void setEnd(int end) {

		this.end = end;

	}

	public void setArr(int[] arr) {

		this.arr = arr;

	}

	public void test(int[] cur){

		if(cur.length==end){

			System.out.println(Arrays.toString(cur));

			return;

		}

		for (int i = 0; i < arr.length; i++) {

			int[] temp = this.mergeIntArray(cur, new int[]{arr[i]});

			test(temp);

		}

	}

	private int[] mergeIntArray(int[] arr1, int[] arr2){

		int[] arr = new int[arr1.length+arr2.length];

		for (int i = 0; i < arr1.length; i++) {

			arr[i] = arr1[i];

		}

		for (int i = 0; i < arr2.length; i++) {

			arr[arr1.length+i] = arr2[i];

		}

		return arr;

	}

	public static void main(String[] args) {

		Test t = new Test();

		int[] i = new int[]{1,2};

		t.setEnd(5);

		t.setArr(i);

		for (int j = 0; j < i.length; j++) {

			t.test(new int[]{i[j]});

		}

	}

}

给定数组a[1,2,3],用a里面的元素来生成一个长度为5的数组，打印出其排列组合的相关教程结束。