import java.util.*; 

public class VettoreSparso {
	
	private int len; 
	
	private HashMap<Integer, Double> map; 
	
	public VettoreSparso(int m) {
		len = m; 
		map = new HashMap<Integer, Double>(); 
	}
	
	public int size() { return len; }
	
	public void put(int i, double x) {
		if(i < 1 || i > len) throw new 
            IndexOutOfBoundsException("index i out of bounds"); 
		map.put(i, x); 
	}
	
	public double get(int i) {
		if(i < 1 || i > len) throw new 
            IndexOutOfBoundsException("index i out of bounds"); 
		if(map.containsKey(i))
			return map.get(i); 
		return 0; 
	}
	
	public Iterable<Integer> indices() {
		return map.keySet(); 
	}
	
	public double dot(VettoreSparso that) {
		double s = 0; 
		for(Integer i : this.indices())
			s += this.get(i) * that.get(i); 
		return s; 
	}
	
	public VettoreSparso plus(VettoreSparso that) {
		VettoreSparso v = new VettoreSparso(len); 
		for(Integer i : this.indices())
			v.put(i, this.get(i)); 
		for(Integer i : that.indices())
			v.put(i, v.get(i) + that.get(i)); 
		return v; 
	}
	
	public String toString() {
		String s = ""; 
		for(int i=1; i<=len; i++)
			s = s + get(i) + " "; 
		return s; 
	}
	
	
}