Java permutation algorithm

Question

Given a collection of integers, what's a Java algorithm that will give combinations as follows..

Given the example collection: [1,3,5], we'd want the output:

[1-1]
[3-3]
[5-5]

[1-3]
[1-5]
[3-5]

Note that ordering is not important, so we want one of [1-3], [3-1] but not both.

This should work with a collection of n numbers, not just the the three numbers as in this example.

Answer 1

Here's the logic you want.

function subsequences (arr) {  
  arr.sort ();
  var subseqs = [];
  for (var i = 0; i < arr.length; ++i) {
    for (var j = i; j < arr.length; ++j) {
      subseqs.push ("" + arr [i] + "-" + arr [j]);
    }
  }
  return subseqs;
}

Answer 2

Below function should do this

  private void printPermutations(int[] numbers) {
    for(int i=0;i<numbers.length; i++) {
      for (int j=i; j<numbers.length; j++) {
        System.out.println("[" + numbers[i] + "-"+ numbers[j] +"]");
      }
    }
  }

Example call to this function

int[] numbers={1,2,3};
printPermutations(numbers);

Answer 3

Sounds like homework...but here it is anyway. Obviously you can do without an ArrayList, etc. - just quick and dirty.

import java.util.ArrayList;

public class Test {

public static void main(String[] args) {
    int[] input = {1, 3, 5};
    ArrayList<String> output = new ArrayList<String>();
    int n = input.length;

    for (int left = 0; left < n; left++) {
        output.add("["+input[left]+"-"+input[left]+"]");
        for (int right = left + 1; right < n; right++) {
            output.add("["+input[left]+"-"+input[right]+"]");
        }
    }

        System.out.println(output.toString());
    }
}