MyHashMap.java

/**
 * 
 * @author Algorithm and Datastructures Team SS2016
 * @version 1.0  
 * 
 */
import java.lang.RuntimeException;
public class MyHashMap {
	
	/**
	 * Use this array to store the values
	 * DO NOT MODIFY OR REMOVE THIS Attribute. Our tests rely on it.
	 */
	private Student[] array;
	protected int capacity;
	protected int hashvalue;
	
	/**
	 * Tries inserting a Student into the hash map.
	 * Throws RunTimeException, if the student is already in the table or the table is full.
	 */
	public void add(Student s){
		array = new Student[capacity];
		
		for(int k = 0; k < array.length; k++) {
			if(array[k] == null) {
				array[k] = s;
				return;
			} else if(array[k].equals(s) || array[k] != null) {
				throw new RuntimeException("error");
			}
		}
		
	}
	
	/**
	 * Try removing a Student from the hash table.
	 * You should use the same implementation for remove discussed in the tutorial.
	 * You should NOT use the lazy deletion strategy (adding a special flag key indicating a deleted key)
	 * See https://en.wikipedia.org/wiki/Linear_probing#Deletion for more details about the algorithm!
	 * Throw RunTimeException if the hash table contained the Student
	 */
	public void remove(Student s){
		// TO DO
		for(Student m : array) {
			if(m == s) {
				throw new RuntimeException("error");
			}
		}
	}
	
	
	/**
	 * Returns true, if the hash table contains the given Student
	 */
	public boolean contains(Student s){
		for(Student i : array) {
			if(i == s) {
				return true;
			} 
		}
		return false;
	}
	
	/**
	 * @param h Hashvalue to search for
	 * @return Number of Student in the hash table that have the hashvalue h
	 */
	public int getNumberStudentsWithHashvalue(int h){
		int n = 0;
	// TO DO 
		
		h = hashvalue;
		array = new Student[capacity];
			
		for(int j = 0; j < array.length; j++) {
			if(array[j].equals(h)) {
				n++;
			}
		}
		return n;
	}
	
	/**
	 * Doubles the size of the hash table. Recomputes the position of all elements using the
	 * new function.
	 */
	public void resize(){
		Student[] newtable = array;
		array = new Student[array.length*2];
		
		for(int n=0; n < array.length; n++) {
			if(array[n] != null) {
				newtable = new Student[array.length*2];
			}
		}
		
	}

	/**
	 * This method return the array in which the strings are stored.
	 * DO NOT MODIFY OR REMOVE THIS METHOD. Our tests rely on it.
	 */
	public Student[] getArray(){
		return array;
	}
	
	/**
	 * DO NOT MODIFY OR REMOVE THIS METHOD. Our tests rely on it.
	 */
	public void setArray(Student[] array){
		this.array = array;
	}

	/**
	 * Runs the hash function for Student s (dependent on the size of the hash table)
	 * DO NOT MODIFY OR REMOVE THIS METHOD. Our tests rely on it.
	 * @param s Student
	 * @return the hash value for a student. (The position where it would be saved given no collisions)
	 */
	public int hashFunction(Student s){
		int hashvalue = Math.abs(s.hashCode()) % array.length;
		return hashvalue;
	}
	
	/**
	 * Constructor to initialize the hash with a given capacity
	 * DO NOT MODIFY OR REMOVE THIS METHOD. Our tests rely on it.
	 */
	public MyHashMap(int capacity){
		array = new Student[capacity];
	}

}