1. Write a Java method removeDuplicates that removes all duplicates in a given list.
Solution:
import java.util.ArrayList;
public class DuplicateTest {
public static void main(String args[])
{
ArrayList<String> list=new ArrayList<String>();
list.add("good");
list.add("better");
list.add("best");
list.add("best");
list.add("first");
list.add("last");
list.add("last");
list.add("last");
list.add("good");
System.out.printf("List Before Duplicate Removal:%s",list);
removeDuplicatesMethod(list);
System.out.printf("\nList After Duplicate Removal:%s",list);
}
private static void removeDuplicatesMethod(ArrayList<String> list) {
// TODO Auto-generated method stub
for(int i=0;i<list.size();i++)
{
for(int k=i+1;k<list.size();k++)
{
if(list.get(i).equals(list.get(k)))
{
list.remove(k);
k--;
}
}
}
}
}
2. Write a Java method testForSum which determines whether a given array of integers contains three entries whose sum is equal to a given integer.
Solution:
public class TestSumImplementation {
public static void main(String args[])
{
int[] testdata={5, 1, 23, 21, 17, 2, 3, 9, 12};
int sum=5;
boolean result= testForSum(testdata,sum);
System.out.print(result);
}
private static boolean testForSum(int[] testdata, int sum) {
// TODO Auto-generated method stub
for(int i=0;i<testdata.length-2;i++)
{
for(int j=i+1;j<testdata.length-1;j++)
{
for(int k=j+1;k<testdata.length;k++ )
if(testdata[i]+testdata[j]+testdata[k]==sum) return true;
}
}
return false;
}
}
3. Create your own linked list
Solution:
public class ListNode {
Object data;
ListNode nextNode;
public ListNode(Object object)
{
data=object;
}
public ListNode(Object object,ListNode Node)
{
data=object;
nextNode=Node;
}
Object getObject()
{
return data;
}
ListNode getNext()
{
return nextNode;
}
}
public class LinkList {
private ListNode firstNode;
private ListNode lastNode;
private String name;
public LinkList()
{
this("list");
}
public LinkList(String listName)
{
name=listName;
}
public void add(Object obj)
{
if(isEmpty())
firstNode=lastNode=new ListNode(obj);
else
firstNode=new ListNode(obj,firstNode);
}
public boolean find(Object obj)
{
if(isEmpty())
return false;
else
{
ListNode current=firstNode;
while(current.nextNode!=null)
{
current=current.nextNode;
if(obj==current.data)
return true;
}
return false;
}
}
public boolean isEmpty()
{
if(firstNode==null)
return true;
else
return false;
}
public String toString()
{
if(isEmpty())
return "Empty List";
else
{
ListNode current=firstNode;
String result="[";
while(current.nextNode!=null)
{
current=current.nextNode;
result+=(String)current.data+",";
}
result+=lastNode.data+"]";
return result;
}
}
public static void main(String args[])
{
LinkList list=new LinkList();
list.add("Straight");
System.out.println(list.toString());
list.add("Bent");
System.out.println(list.toString());
list.add("Equals");
System.out.println(list.toString());
list.add("Well");
System.out.println(list.toString());
list.add("Storm");
System.out.println(list.toString());
//System.out.println(list.toString());
System.out.printf("\nSearch result of well:%s",list.find("Well"));
System.out.printf("\nSearch result of Strength:%s",list.find("Strength"));
}
}
4. Permutation:
import java.util.ArrayList;
import java.util.LinkedList;
public class Permutation {
public static void main(String[] args) {
for(int[] a :permutationsOf(new int[]{1,2,3,4})){
for(int b:a){
System.out.print(b+",");
}
System.out.println();
}
}
static ArrayList<int[]> permutationsOf(int[] arr) {
ArrayList<int[]> result = new ArrayList<int[]>();
if (arr.length == 1) {
result.add(arr);
return result;
} else {
int first=arr[0];
int[] rest=new int[arr.length-1];
for(int i=1;i<arr.length;i++){
rest[i-1]=arr[i];
}
ArrayList<int[]> simpler=permutationsOf(rest);
for(int[] permutation:simpler){
ArrayList additions=insertAtAllPositions(first,permutation);
result.addAll(additions);
}
return result;
}
}
private static ArrayList insertAtAllPositions(int first, int[] permutation) {
// TODO Auto- generated method stub
ArrayList<int[]> res=new ArrayList<int[]>();
for(int i=0;i<permutation.length+1;i++){
LinkedList<Integer> ll=new LinkedList<Integer>();
for(int j=0;j<permutation.length;j++){
ll.add(permutation[j]);
}
ll.add(i, first);
int[] r=new int[ll.size()];
int count=0;
for(int z:ll){
r[count++]=z;
}
res.add(r);
}
return res;
}
}
5. Object Restriction:
public class RestrictInstance {
private static final int limit_ =5; //Set this to whatever you want to restrict
private static int count =0;
private RestrictInstance(){}
public static synchronized RestrictInstance getInstance(){
if(count<limit_){
RestrictInstance myClass= new RestrictInstance();
count++;
return myClass;
}
return null;
}
public static void main(String args[])
{
RestrictInstance a= RestrictInstance.getInstance();
RestrictInstance a1= RestrictInstance.getInstance();
RestrictInstance a2= RestrictInstance.getInstance();
RestrictInstance a3= RestrictInstance.getInstance();
RestrictInstance a4= RestrictInstance.getInstance();
RestrictInstance a5= RestrictInstance.getInstance();
System.out.println(a.toString());
System.out.println(a3.toString());
System.out.println(a4.toString());
//System.out.println(a5.toString());
}
}
Solution to problem 1
package prob1;
public class MyStringList {
private int size
= 0;
private final int
INIT_ARR_SIZE = 2;
private String[]
strArray;
public
MyStringList(){
strArray =
new String[INIT_ARR_SIZE];
}
public void
add(String s) {
if(size
>= strArray.length) resize();
strArray[size++]=s;
}
public boolean
find(String s) {
for(int i =
0; i < size; ++i) {
if(s.equals(strArray[i]))
return true;
}
return
false;
}
public String
get(int i) {
if(i < 0
|| i >= size) return null;
return
strArray[i];
}
private void
resize() {
System.out.println("Resizing
from size "+strArray.length +"to "+2*strArray.length);
String[]
temp = new String[2*strArray.length];
for(int i =
0; i < strArray.length; ++i) {
temp[i]
= strArray[i];
}
strArray =
temp;
}
public static
void main(String[] args) {
MyStringList
list = new MyStringList();
for(int i =
0; i < 64; ++i) {
list.add("a"+i);
}
System.out.println("looking
for a3 "+list.find("a3"));
System.out.println("value
at position 43 "+list.get(43));
}
}
Solution to Problem 2
package prob2;
import java.util.HashMap;
import java.util.Iterator;
public class Employee {
private String
firstName;
private String
lastName;
private HashMap
salaryRecord=new HashMap();
public void
addEntry(String date, double salary) {
salaryRecord.put(date,salary);
}
public void
printPaymentAmount(String date) {
Double
salaryObject = (Double)salaryRecord.get(date);
if(salaryObject
== null){
System.out.println(firstName+"
"+lastName+" did not receive a paycheck on "+date);
}
else {
System.out.println(firstName+"
"+lastName+" was paid "+salaryObject.doubleValue()+" on
"+date);
}
}
public void
printAveragePaycheck() {
Iterator it
= salaryRecord.keySet().iterator();
double
accum = 0.0;
int count =
0;
while(it.hasNext()){
String
nextDate = (String)it.next();
Double
sal = (Double)salaryRecord.get(nextDate);
accum
+= sal.doubleValue();
++count;
}
System.out.println("Average
paycheck for "+firstName+" "+lastName+" was
"+accum/count);
}
public static
void main(String[] args) {
Employee e
= new Employee();
e.setFirstName("Jim");
e.setLastName("Jones");
for(int i =
0; i < 12; ++i) {
e.addEntry(i+"/15/2006",
3070+5*i);
}
e.printPaymentAmount("3/15/2006");
e.printPaymentAmount("5/15/2005");
e.printAveragePaycheck();
}
public String
getFirstName() {
return
firstName;
}
public void
setFirstName(String firstName) {
this.firstName
= firstName;
}
public String
getLastName() {
return
lastName;
}
public void
setLastName(String lastName) {
this.lastName
= lastName;
}
}