import java.util.*;

public class sparseVector {

int size;

// store index : value

Map<Integer, Integer> map;

public sparseVector(int size){

this.size = size;

this.map = new HashMap<>();

}

public void set(int index, int value){

if(index >= size){

throw new java.lang.Error("out of index!");

}

map.put(index, value);

}

public String toString(){

StringBuilder sb = new StringBuilder();

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

if(map.containsKey(i)){

sb.append(map.get(i));

}else{

sb.append("0");

}

sb.append(",");

}

return sb.toString();

}

// add operation

public sparseVector add(sparseVector v){

if(v.size != size){

throw new java.lang.Error("Vectors length don't match");

}

sparseVector v3 = new sparseVector(v.size);

for(Map.Entry<Integer,Integer> entry : map.entrySet()){

int index = entry.getKey();

int value = entry.getValue();

v3.map.put(index, v3.map.getOrDefault(index, 0)+value);

}

for(Map.Entry<Integer,Integer> entry : v.map.entrySet()){

int index = entry.getKey();

int value = entry.getValue();

v3.map.put(index, v3.map.getOrDefault(index, 0)+value);

}

System.out.println(v3.toString());

return v3;

}

public static void main(String[] args){

sparseVector v1 = new sparseVector(5);

v1.set(0, 4);

v1.set(1, 5);

sparseVector v2 = new sparseVector(5);

v2.set(1, 2);

v2.set(3,3);

v1.add(v2);

}

}