CODEWITHSUNDEEP
javaarrays
coder101
coder101

Reputation: 850

All possible Subsequences of an array using java

I intend to find all possible subsequences of an array

I tried to do it in 2 different ways

1) Method 1

I create a string with the values in array

// all possible subsequences - all possible elements found by eleiminating zero or more characters

Public class StrManipulation{

public static void combinations(String suffix,String prefix){
    if(prefix.length()<0)return;
    System.out.println(suffix);
    for(int i=0;i<prefix.length();i++)
     combinations(suffix+prefix.charAt(i),prefix.substring(i+1,prefix.length()));
}

public static void main (String args[]){
    combinations("","12345");
    }
 }

Problem --- works only for single digit characters

2) Method 2

    int a[] = new int[3];
    a[0]=2;a[1]=3;a[2]=8;

  List<Integer> al= new ArrayList<Integer>();

    for(int i=0;i<3;i++)
        al.add(a[i]);

  int i, c;

  for( c = 0 ; c < 3 ; c++ )
  {

     for( i = c+1 ; i <= 3 ; i++ )
     {   

         List<Integer> X = al.subList(c,i);

         for(int z=0;z<X.size();z++)
             System.out.print(X.get(z)+" ");

         System.out.println();
     }
  }

Problem -- It generates subarrays only for example for an array 2 5 9 I get ---- [2] [2,5] [2,5,9] [5] [5,9] [9] But it misses [2,9]

So can anyone help me with this code?

Upvotes: 1

Views: 9069

Answers (1)

maraca
maraca

Reputation: 8743

Here is a code snippet, the idea: add the element to the sequence and to all previous ones, is it what you want? It is not checked if a sequence already exists.

public List<List<Integer>> combinations(int[] arr) {
    List<List<Integer>> c = new ArrayList<List<Integer>>();
    List<Integer> l;
    for (int i = 0; i < arr.length; i++) {
      int k = c.size();
      for (int j = 0; j < k; j++) {
        l = new ArrayList<Integer>(c.get(j));
        l.add(new Integer(arr[i]));
        c.add(l);
      }
      l = new ArrayList<Integer>();
      l.add(new Integer(arr[i]));
      c.add(l);
    }
    return c;
}

Upvotes: 7

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