Java Program to Implement Sparse Vector

This is a Java Program to implement Sparse Vector. Sparse vectors are useful implementation of vectors that mostly contains zeroes. Here sparse vectors consists of (index, value) pairs.

Here is the source code of the Java Program to implement Sparse Vector. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

```
/**
```

 ** Java Program to implement Sparse Vector

```
 **/
```
```
 
```
```
import java.util.Scanner;
```
```
import java.util.TreeMap;
```
```
import java.util.Map;
```
```
 
```
```
/** Class SparseVector **/
```
```
class SparseVector
```
```
{
```

	/* Tree map is used to maintain sorted order */

    private TreeMap<Integer, Double> st;

```
    private int N;
```
```
 
```
```
    /** Constructor **/
```
```
    public SparseVector(int N)
```
```
    {
```
```
        this.N = N;
```

        st = new TreeMap<Integer, Double>();

```
    }
```
```
 
```

    /** Function to insert a (key, value) pair **/

    public void put(int i, double value)

```
    {
```
```
        if (i < 0 || i >= N) 
```

               throw new RuntimeException("\nError : Out of Bounds\n");

```
 
```
```
        if (value == 0.0) 
```
```
            st.remove(i);
```
```
        else
```
```
            st.put(i, value);
```
```
    }
```
```
 
```

    /** Function to get value for a key **/

```
    public double get(int i) 
```
```
    {
```
```
        if (i < 0 || i >= N) 
```
```
        {
```

            throw new RuntimeException("\nError : Out of Bounds\n");

```
        }
```
```
        if (st.containsKey(i)) 
```
```
            return st.get(i);
```
```
        else                
```
```
            return 0.0;
```
```
    }
```
```
 
```

    /** Function to get size of the vector **/

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    public int size() 
```
```
    {
```
```
        return N;
```
```
    }
```
```
 
```

    /** Function to get dot product of two vectors **/

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    public double dot(SparseVector b) 
```
```
    {
```
```
        SparseVector a = this;
```
```
        if (a.N != b.N) 
```

               throw new RuntimeException("Error : Vector lengths are not same");

```
 
```
```
        double sum = 0.0;
```
```
 
```

        if (a.st.size() <= b.st.size())

```
        {
```

            for (Map.Entry<Integer, Double> entry : a.st.entrySet())

                if (b.st.containsKey(entry.getKey()))

                    sum += a.get(entry.getKey()) * b.get(entry.getKey());

```
        }          
```
```
        else  
```
```
        {
```

            for (Map.Entry<Integer, Double> entry : b.st.entrySet())

                if (a.st.containsKey(entry.getKey()))

                    sum += a.get(entry.getKey()) * b.get(entry.getKey());

```
        }
```
```
        return sum;
```
```
    }
```
```
 
```

    /** Function to get sum of two vectors **/

    public SparseVector plus(SparseVector b)

```
    {
```
```
        SparseVector a = this;
```
```
        if (a.N != b.N) 
```

               throw new RuntimeException("Error : Vector lengths are not same");

```
 
```

        SparseVector c = new SparseVector(N);

```
 
```

        for (Map.Entry<Integer, Double> entry : a.st.entrySet())

            c.put(entry.getKey(), a.get(entry.getKey()));

```
 
```

        for (Map.Entry<Integer, Double> entry : b.st.entrySet())

            c.put(entry.getKey(), b.get(entry.getKey()) + c.get(entry.getKey()));

```
 
```
```
        return c;
```
```
    }
```
```
 
```

    /** Function toString() for printing vector **/

```
    public String toString() 
```
```
    {
```
```
        String s = "";
```

        for (Map.Entry<Integer, Double> entry : st.entrySet())

            s += "(" + entry.getKey() + ", " + st.get(entry.getKey()) + ") ";

```
 
```
```
        return s;
```
```
    }
```
```
}
```
```
 
```
```
/** Class SparseVector **/
```
```
public class SparseVectorTest
```
```
{
```

    public static void main(String[] args)

```
    {
```

        System.out.println("Sparse Vector Test\n");

        Scanner scan = new Scanner(System.in);

```
 
```

        System.out.println("Enter size of sparse vectors");

```
        int n = scan.nextInt();
```
```
 
```

        SparseVector v1 = new SparseVector(n);

        SparseVector v2 = new SparseVector(n);

```
 
```

        System.out.println("\nEnter number of entries for vector 1");

```
        int n1 = scan.nextInt();
```

        System.out.println("Enter "+ n1 +" (int, double) pairs");

```
        for (int i = 0; i < n1; i++)
```

            v1.put(scan.nextInt(), scan.nextDouble() );

```
 
```

        System.out.println("\nEnter number of entries for vector 2");

```
        int n2 = scan.nextInt();
```

        System.out.println("Enter "+ n2 +" (int, double) pairs");

```
        for (int i = 0; i < n2; i++)
```

            v2.put(scan.nextInt(), scan.nextDouble() );

```
 
```
```
        System.out.println("\n");
```

        System.out.println("Vector v1 = " + v1);

        System.out.println("Vector v2 = " + v2);

        System.out.println("\nv1 dot v2 = " + v1.dot(v2));

        System.out.println("v1  +  v2   = " + v1.plus(v2));

```
    }
```
```
}
```

Sparse Vector Test
 
Enter size of sparse vectors
70000
 
Enter number of entries for vector 1
4
Enter 4 (int, double) pairs
3 1.0
2500 6.3
5000 10.0
60000 5.7
 
Enter number of entries for vector 2
3
Enter 3 (int, double) pairs
1 7.5
3 5.7
2500 -6.3
 
 
Vector v1 = (3, 1.0) (2500, 6.3) (5000, 10.0) (60000, 5.7)
Vector v2 = (1, 7.5) (3, 5.7) (2500, -6.3)
 
v1 dot v2 = -33.989999999999995
v1  +  v2   = (1, 7.5) (3, 6.7) (5000, 10.0) (60000, 5.7)

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