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Tuesday 7 July 2015

Java Important Interview Programs - 2

9. Write a program to implement ArrayList.


Description:
Write a program to implement your own ArrayList class. It should
contain add(), get(), remove(), size() methods. Use dynamic array logic.
It should increase its size when it reaches threshold.

Code:
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package kundan;
 
import java.util.Arrays;
 
public class MyArrayList {
 
    private Object[] myStore;
    private int actSize = 0;
     
    public MyArrayList(){
        myStore = new Object[10];
    }
     
    public Object get(int index){
        if(index < actSize){
            return myStore[index];
        } else {
            throw new ArrayIndexOutOfBoundsException();
        }
    }
     
    public void add(Object obj){
        if(myStore.length-actSize <= 5){
            increaseListSize();
        }
        myStore[actSize++] = obj;
    }
     
    public Object remove(int index){
        if(index < actSize){
            Object obj = myStore[index];
            myStore[index] = null;
            int tmp = index;
            while(tmp < actSize){
                myStore[tmp] = myStore[tmp+1];
                myStore[tmp+1] = null;
                tmp++;
            }
            actSize--;
            return obj;
        } else {
            throw new ArrayIndexOutOfBoundsException();
        }
         
    }
     
    public int size(){
        return actSize;
    }
     
    private void increaseListSize(){
        myStore = Arrays.copyOf(myStore, myStore.length*2);
        System.out.println("\nNew length: "+myStore.length);
    }
     
    public static void main(String a[]){
        MyArrayList mal = new MyArrayList();
        mal.add(new Integer(2));
        mal.add(new Integer(5));
        mal.add(new Integer(1));
        mal.add(new Integer(23));
        mal.add(new Integer(14));
        for(int i=0;i<mal.size();i++){
            System.out.print(mal.get(i)+" ");
        }
        mal.add(new Integer(29));
        System.out.println("Element at Index 5:"+mal.get(5));
        System.out.println("List size: "+mal.size());
        System.out.println("Removing element at index 2: "+mal.remove(2));
        for(int i=0;i<mal.size();i++){
            System.out.print(mal.get(i)+" ");
        }
    }
}

Output:
2 5 1 23 14 
New length: 20
Element at Index 5:29
List size: 6
Removing element at index 2: 1
2 5 23 14 29

10. Write a program to find out duplicate characters in a string.


Description:
Write a program to find out duplicate or repeated characters in a
string, and calculate the count of repeatation.

Code:
package kundan;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class DuplicateCharsInString {

 public void findDuplicateChars(String str){
  
  Map<Character, Integer> dupMap = new HashMap<Character, Integer>(); 
  char[] chrs = str.toCharArray();
  for(Character ch:chrs){
   if(dupMap.containsKey(ch)){
    dupMap.put(ch, dupMap.get(ch)+1);
   } else {
    dupMap.put(ch, 1);
   }
  }
  Set<Character> keys = dupMap.keySet();
  for(Character ch:keys){
   if(dupMap.get(ch) > 1){
    System.out.println(ch+"--->"+dupMap.get(ch));
   }
  }
 }
 
 public static void main(String a[]){
  DuplicateCharsInString dcs = new DuplicateCharsInString();
  dcs.findDuplicateChars("kundan");
 }
}

Output:
n--->2

11. Write a program to find top two maximum numbers in a array.


Description:
Write a program to find top two maximum numbers in the
given array. You should not use any sorting functions. You
should iterate the array only once. You should not use any
kind of collections in java.

Code:
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package kundan;
 
public class TwoMaxNumbers {
 
    public void printTwoMaxNumbers(int[] nums){
        int maxOne = 0;
        int maxTwo = 0;
        for(int n:nums){
            if(maxOne < n){
                maxTwo = maxOne;
                maxOne =n;
            } else if(maxTwo < n){
                maxTwo = n;
            }
        }
        System.out.println("First Max Number: "+maxOne);
        System.out.println("Second Max Number: "+maxTwo);
    }
     
    public static void main(String a[]){
        int num[] = {5,34,78,2,45,1,99,23};
        TwoMaxNumbers tmn = new TwoMaxNumbers();
        tmn.printTwoMaxNumbers(num);
    }
}

Output:
First Max Number: 99
Second Max Number: 78

12. Write a program to sort a map by value.


Description:
Sort or order a HashMap or TreeSet or any map item by value. Write a comparator
which compares by value, not by key. Entry class might hleps you here.

Code:
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package kundan;
 
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;
 
public class OrderByValue {
 
    public static void main(String a[]){
        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("java", 20);
        map.put("C++", 45);
        map.put("Unix", 67);
        map.put("MAC", 26);
        map.put("Why this kolavari", 93);
        Set<Entry<String, Integer>> set = map.entrySet();
        List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>(set);
        Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
        {
            public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
            {
                return (o2.getValue()).compareTo( o1.getValue() );
            }
        } );
        for(Map.Entry<String, Integer> entry:list){
            System.out.println(entry.getKey()+" ==== "+entry.getValue());
        }
    }
}

Output:
Why this kolavari ==== 93
Unix ==== 67
C++ ==== 45
MAC ==== 26
java ==== 20

13. Write a program to find common elements between two arrays.


Description:
Write a program to identify common elements or numbers between
two given arrays. You should not use any inbuilt methods are list to
find common values.

Code:
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package kundan;
 
public class CommonElementsInArray {
 
    public static void main(String a[]){
        int[] arr1 = {4,7,3,9,2};
        int[] arr2 = {3,2,12,9,40,32,4};
        for(int i=0;i<arr1.length;i++){
            for(int j=0;j<arr2.length;j++){
                if(arr1[i]==arr2[j]){
                    System.out.println(arr1[i]);
                }
            }
        }
    }
}

Output:
4
3
9
2

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