Java Interviews Frequently Asked Puzzles

Interview puzzles is the best way to check person's analytical skills. In investment banking job you need analytical skill to perform day to day job. It is not only applicable to traders , but some level of analytical skills is required by people who are developing these systems for understand business. Now a days it is become common practice to ask 1-2 puzzles during investment bank interview to check the candidate's analytical skills. The best way to clear this round is practice common puzzles and understand the logic to solve them. 

1) Fibonacci in Java:
The input will be number n and the output should be sum for 0 to n. for example
for n =4 the result should be 0+1+2+3+4 = 10
public class FibonacciNumber {
public static int fibonacci(int n) {
if (n < 2) {
return n;
}
else {
return fibonacci(n-1)+fib(n-2);
}
}
}
view raw Fibbonacci.java hosted with ❤ by GitHub

2) String Reverse
The input String "abcde" should return "edcba".
public reverse(String word) {
char[] chs = word.toCharArray();
int i=0, j=chs.length-1;
while (i < j) {
// swap chs[i] and chs[j]
char t = chs[i];
chs[i] = chs[j];
chs[j] = t;
i++; j--;
}
}
//Another way using java utility.
import org.apache.commons.lang.StringUtils;
String reverseWords(String sentence) {
return StringUtils.reverseDelimited(StringUtils.reverse(sentence), ' ');
}

3) Reversing a linked list in Java
Here is example of revering the linked list in java using recursive function:
public class ListNode {
String data = "";
ListNode next = null;
public ListNode(String data, ListNode node) {
this.data = data;
this.next = node;
}
// reverse
public static ListNode reverse (ListNode list){
if (list == null) return null;
if (list.next == null) return list;
ListNode secondElem = list.next;
list.next = null;
ListNode reverseRest = reverse(secondElem);
secondElem.next = list;
return reverseRest;
}
public static void main(String[] args) {
ListNode node3= new ListNode ("node3",null);
ListNode node2= new ListNode ("node2",node3);
ListNode node1= new ListNode ("node1",node2);
System.out.println(" Last Item : "+node1.next.next.data+"\n");
ListNode reverseList = ListNode.reverse(node1);
System.out.println("First Item "+reverseList.data);
}
}
view raw listNode.java hosted with ❤ by GitHub

4) Find the missing number in Java
You have an array of numbers from 1 to 100 (both inclusive). The size of the array is 100. The numbers are randomly added to the array, but there is one random empty slot in the array. What is the quickest way to find that slot as well as the number that should be put in the slot?
Try it for practice. please suggest the answer .
[Trick sum of n numbers is n*(n+1)/2]
import java.util.*;
public class MissingNumber {
public static void main(String...strings){
Set numberSet = new HashSet();
// Max number in the sequence
int k = 50;
// put the numbers
for(int i=0;i<=50;i++){
numberSet.add(i);
}
// Remove random number
int i = (new Random()).nextInt(50);
System.out.println(" Removing number -->"+i);
numberSet.remove(i);
// find the current sum
int sum =0;
for(int m : numberSet){
sum= sum +m;
}
// Find the missing number
int l = ((k)*((k+1))/2)- sum;
System.out.println(" Missing number -->"+l);
}
}


5) Write a substring function in Java
String test= "AA BB CC BB BB CC BB";
String[]{"BB", "CC", "AA"}
Result shd be BB=4; CC=2 and AA=1
Since B occurred 4 times C did 2 times and A only 1 time.
This basic problem can be asked in different ways like, You have multiple words in new paper and find out the frequency of words in one page of news paper?
public static String[] sortingData(String data) {
String[] strings = data.split(" ");
// Finding distinct values
HashMap map = new HashMap();
for (String s : strings) {
Integer i = map.get(s);
if (i != null) {
map.put(s, i+1);
} else {
map.put(s, 1);
}
}
// Ordering using Collections
TreeMap sort = new TreeMap(Collections.reverseOrder());
for (Entry e : map.entrySet()) {
sort.put(e.getValue(), e.getKey());
}
return sort.values().toArray(new String[0]);
}

6) Reverse a String in Java
Reverse the String by java function without recursion and with recursion
//Reverse the String by java function without recursion
public static String reverseString(String str){
if(str==null || str.length()==1)
return str;
int i = str.length();
char[] reverse = new char[i];
for(int j=0;j;j++)
reverse[j]= str.charAt(i-j-1);
}
return new String(reverse);
}
//Reverse the String by java function with Recursive Function
public static String reverse(String str) {
if ((null == str) || (str.length() <= 1)) {
return str;
}
return reverse(str.substring(1)) + str.charAt(0);
}

7) Find one string inside another in Java
We can use String.indexOf( subString ) and it will return the first index of substring;
for Last Index : lastIndexOf(String str)

8) Algo for finding largest number in Array of Integer
Easy one, Check the integer one by one and find the largest number.

9) Java Runtime method invocation question:
Example : Tell the output of this
class Base {
protected int i;
Base() {
add(1);
}
void add(int v) {
i += v;
}
}
class Extension extends Base {
Extension() {
add(1);
}
void add(int v) {
i += v * 2;
}
}
public class Example {
public static void main(String[] args) {
System.out.println(" " + bogo(new Extension()));
}
static int bogo(Base b) {
return b.add(8);
}
}
Answer is : 20 .

10) Suppose you have a large file with lots of words. How would you find the unique words and their count? What kind of data structure u will use? What will be the time complexity and space complexity?
We need to take care of two things counting the words and second duplicate. the best performance will be using hash function.
import java.util.*;
public class Freq {
public static void main(String[] args) {
Map m = new HashMap();
// Initialize frequency table from command line
for (String a : args) {
Integer freq = m.get(a);
m.put(a, (freq == null) ? 1 : freq + 1);
}
System.out.println(m.size() + " distinct words:");
System.out.println(m);
}
}


11) A train is one mile long. It travels at the rate of one mile a minute through a tunnel which is also one mile long. Can you say how long it will take for the train to pass completely through the tunnel? 

Answer : 2 minutes

it will take two minutes if you count the time for it to completely pass through the tunnel. One minute to pass through the tunnel and another one minute to drag itself out of the tunnel completely so two minutes nice question though well logical.



12) Convert String = "98989" into an integer without using any library functions in java.
Give fastest way to do it and explain why your method is best.
// converting string to number using ascii code
// converting string to number using ascii code
public static int convertStringToInt(String num){
int result=0;
int zeroAscii=48;
int nineAscii=57;
for(char c: num.toCharArray()){
if(c>=zeroAscii && c<=nineAscii){
result=result*10+(c-zeroAscii);
}else
return -1;
}
return result;
}


13) Write a program to shuffle a deck of 52 cards and shuffle them equally to 4 players.

package com.learning.puzzle;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;
/*
* Write the code to shuffle a deck of 52 cards,
* and shuffle them equally to 4 players
*/
class Card {
public enum Rank {
DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE
}
public enum Suit {
CLUBS, DIAMONDS, HEARTS, SPADES
}
private final Rank rank;
private final Suit suit;
private Card(Rank rank, Suit suit) {
this.rank = rank;
this.suit = suit;
}
public Rank rank() {
return rank;
}
public Suit suit() {
return suit;
}
public String toString() {
return rank + " of " + suit;
}
private static final List<Card> protoDeck = new ArrayList<Card>();
// Initialize prototype deck
static {
for (Suit suit : Suit.values())
for (Rank rank : Rank.values())
protoDeck.add(new Card(rank, suit));
}
public static ArrayList<Card> newDeck() {
return new ArrayList<Card>(protoDeck); // Return copy of prototype deck
}
}
public class RandomCards {
private Map<Integer, ArrayList<Integer>> map = new HashMap<Integer, ArrayList<Integer>>();
public RandomCards() {
}
public static void main(String[] args) {
ArrayList<Card> player1 = new ArrayList<Card>();
ArrayList<Card> player2 = new ArrayList<Card>();
ArrayList<Card> player3 = new ArrayList<Card>();
ArrayList<Card> player4 = new ArrayList<Card>();
ArrayList<Card> deck = Card.newDeck();
Random random = new Random();
int j = 1;
for (int i = 0; i < 52; i++) {
int temp = random.nextInt(52);
if (j == 1) {
player1.add(deck.get(i));
j++;
continue;
} else if (j == 2) {
player2.add(deck.get(i));
j++;
continue;
} else if (j == 3) {
player3.add(deck.get(i));
j++;
continue;
} else if (j == 4) {
player4.add(deck.get(i));
j = 1;
continue;
}
}
System.out.println(" Player 1 " + player1);
System.out.println(" Player 2 " + player2);
System.out.println(" Player 3 " + player3);
System.out.println(" Player 4 " + player4);
}
}
view raw gistfile1.java hosted with ❤ by GitHub
Answer this puzzle by comments.
Given n stairs, how many number of ways can you climb if u use either 1 or 2 at a time?
for example you have 4 stairs and you can climb like
1,1,1,1
1,1,2
1,2,1
2,1,1
2,2
so in overall 5 ways for 3 stairs.

26 comments:

  1. Replies
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  2. The problem statement of "4) Find the missing number" is vague, could you please refine / clarify it?

    ReplyDelete
    Replies
    1. In Java 1.6 uses the Generics.....to put like this
      Set numberSet = new HashSet();

      Delete
    2. In java using the generics


      package com.bangalore;

      import java.util.HashSet;
      import java.util.Random;
      import java.util.Set;

      public class MissingNumber {

      public static void main(String...strings){
      Set num = new HashSet();
      // Max number in the sequence
      int k = 50;
      // put the numbers
      for(int i=0;i<=50;i++){
      num.add(i);
      }
      // Remove random number
      int i = (new Random()).nextInt(50);
      System.out.println(" Removing number -->"+i);
      num.remove(i);
      // find the current sum
      int sum =0;
      for(int m : num){
      sum= sum +m;
      }
      // Find the missing number
      int l = ((k)*((k+1))/2)- sum;
      System.out.println(" Missing number -->"+l);
      }

      }

      Delete
  3. The first example seems different from fibonacci series. If It is 0+1+2+3+4 +.. n
    Shouldnt it be

    private static int getSeriesResut(int n) {

    int sum = 0;
    for (int i = 1; i <= n; i++) {
    sum = sum + i;
    }
    return sum;

    }

    ReplyDelete
    Replies
    1. This comment has been removed by the author.

      Delete
  4. This comment has been removed by the author.

    ReplyDelete
    Replies
    1. This comment has been removed by the author.

      Delete
  5. For Fibonacci Series ... using iteration seems to be much more performant than recursion.
    Both methods are compared here: https://gist.github.com/josseyj/9062009

    ReplyDelete
  6. the card suffling example will give the same result every time you run it as you are neither suffling the deck nor using the temp variable.
    adding Collections.shuffle(deck) would sufficce for your example

    ReplyDelete
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  9. Question 9:
    It has compilation errors.The methods add in base and derived class have return type void.

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  11. Good Collection I do not know Why you have not given these JAVA Puzzles (Almost All Companies Ask these)
    You can read from here

    http://codinginterviewquestionsans.blogspot.com/2018/03/java-puzzles-expressive-puzzlers.html

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  14. Find Missing Number Java simple code ::

    package Code_brush_Up;

    import java.util.Scanner;

    public class FindMissingNumber {
    public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int arr[] = new int[n-1]; //the length of the array should be n-1
    for(int i = 0;i<arr.length;i++){
    arr[i] = sc.nextInt();
    }
    int totalN = n*(n+1)/2; //to find the sum of 1 to n
    int totalArrSum =0;
    for(int i = 0;i<arr.length;i++){ //to find the sum of all element in array
    totalArrSum += arr[i];
    }
    int diff = totalN - totalArrSum;
    System.out.println("Missing elemtn is "+diff);
    }
    }

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