String Questions

1. How to find the Longest Substring in String
2. Swapping Letters in 2 Words
3. Print String in Reverse Order
4. Print Left Right Angle Triangle
5. Inverted Right Triangle
6. Print Right Angle Triangle
7. Print Pyramid
8. Sum of Pairs in Array of Numbers
9. Check 2nd List has all elements in 1st List
10. How to find String is anagram
11. Check Palindrome
12. Reverse of String without for loop and array
13. Check Palindrome with recursion

1.How to find the Longest Substring in String
Input

String strSample = "ABCAAABCD"

Output

ABCD

public static void main(String[] args) 
{
   String Test = "ABCAAABCD";
   String dummy = ""; 
		
   String[] arrTest = Test.split("");
		
   List<String> seenChars = new ArrayList<String>();
   List<String> subStrings = new ArrayList<String>();
		
   int j = 0;
		
   for (int i = 1; i < arrTest.length; i++) 
   {
      if(seenChars.contains(arrTest[i]))
      {
	 subStrings.add(dummy);
	 dummy = "";
	 seenChars.clear();
      }
			
      seenChars.add(arrTest[i]);
      dummy += arrTest[i];
			
       j = i + 1;
			
       if(j == arrTest.length)
	  subStrings.add(dummy);
   }
		
   int highestNo = 0;
   int lastHighest = 0;
   int currHighestNo = 0;
   int highestPOS = 0;
	
   for(int k = 0; k < subStrings.size() ; k++)
   {
	currHighestNo = subStrings.get(k).length();
		
	if(currHighestNo  > lastHighest)
	{
  	  highestNo = currHighestNo;
	  highestPOS = k;
	}		
	  lastHighest = currHighestNo;
	}
		
	System.out.println(subStrings.get(highestPOS));		
}

Method 2

public static void main(String args[]) 
{
	String Test = "ABCDEAAABCDA";
	String dummy = "";

	String[] arrTest = Test.split("");
	String longestSubString = "";

	List<String> seenChars  = new ArrayList<String>();
	List<String> subStrings = new ArrayList<String>();

	for (String strTest : arrTest) 
	{
		if (seenChars.contains(strTest)) 
		{
			if (dummy.length() > longestSubString.length())
				longestSubString = dummy;

			subStrings.add(dummy);
			dummy = "";
			seenChars.clear();
		}
		
		seenChars.add(strTest);
		dummy += strTest;
	}
	
	if (dummy.length() > longestSubString.length())
	{
		longestSubString = dummy;		
		subStrings.add(dummy);	
	}
	 
	System.out.println("Longest subString is: " + "'" + longestSubString + "'" + " and length is: "
			+ longestSubString.length());
}

2.Swapping Letters in 2 Words
Input

MUGIL XXX

Output

MXUXGXIL

public class Array1 
{
 static List arrNewList1 = new ArrayList();
 
 public static void main(String[] args) 
 { 
   String text1 = "MUGIL";
   String text2 = "XXX"; 
 
   String[] arrList1 = text1.split("");
   String[] arrList2 = text2.split("");
 
   if(arrList2.length > arrList1.length)
    swapArrays(arrList2, arrList1);
   else 
    swapArrays(arrList1, arrList2);

 
 
   StringBuilder strBr = new StringBuilder();
 
   for (int i = 0; i < arrNewList1.size(); i++) 
    strBr.append(arrNewList1.get(i));
 
    System.out.println(strBr); 
 }
 
 public static void swapArrays(String[] pBigList, String[] pSmallList)
 { 
   for (int i = 0; i < pBigList.length; i++) 
   { 
     arrNewList1.add(pBigList[i]);
 
     if(i < pSmallList.length)
      arrNewList1.add(pSmallList[i]);
   }
 }
}

Note

 .
 .
 String Text1 = "M,U,G,I,L";
 String Text2 = "MUGIL";
		
 System.out.println(Text1.split(",").length);
 System.out.println(Text2.split("").length);
 .
 .

Output

5
6

you may be puzzled why first prints 5 and second prints 6.Thats because the empty space between “M is taken as 1 element in Text2

3.Print String in Reverse Order
Input

asanam

Output

asanam

package com.mugil.test;

public class ReverseString {

 public static void main(String[] args) {
  String strName = "manasa";

  //char[] arrNames = strName.toCharArray();

  String[] arrNames = strName.split("");

  for (int i = arrNames.length - 1; i >= 0; i--) {
   System.out.print(arrNames[i]);
  }
 }
}

4.Print Left Right Angle Triangle
Input

Total number of Rows - 5

Output

* 
** 
*** 
**** 
***** 

package com.mugil.test;

public class Patterns2 {
 public static void main(String[] args) {
  int rows = 5;

  for (int i = 1; i <= rows; i++) {
   for (int j = 1; j <= i; j++) {
    System.out.print("*");
   }

   System.out.println(" ");
  }
 }
}

5.Inverted Right Triangle
Input

Total number of Rows - 5

Output

***** 
**** 
*** 
** 
*  

.
int rows = 5;

for (int i = rows; i >= 0; i--) {
 for (int j = 1; j <= i; j++)
  System.out.print("*");

 System.out.println(" ");
}
.

6.Print Right Angle Triangle
Input

Total number of Rows - 5

Output

     * 
    ** 
   *** 
  **** 
 *****  

int n = 5;
int j = 0;
int k = 0;

for (int i = 0; i < n; i++) {
 for (j = n - i; j > 1; j--)
  System.out.print(" ");

 for (j = 0; j <= i; j++)
  System.out.print("*");

 System.out.println();

}

7.Print Pyramid
Input

Total number of Rows - 5

Output

    * 
   * * 
  * * * 
 * * * * 
* * * * *  

int n = 5;
int j = 0;
int k = 0;

for (int i = 0; i < n; i++) 
{
 for (j = n - i; j > 1; j--)
  System.out.print(" ");

 for (j = 0; j <= i; j++)
  System.out.print("* ");

 System.out.println();

}

The only Difference between Right Angle Triangle and Pyramid is Space in *

8.Sum of Number Pairs in Array
Input

Array of Numbers - {0,1,2,2,3,4}
Sum - 4

Output

(0,4)
(1,3)
(2,2)

.
Integer[] arrNumbers = { 0, 1, 2, 2, 3, 4, 5};
int sum = 4;

for (int i = 0; i < arrNumbers.length; i++) {
 for (int j = i + 1; j < arrNumbers.length; j++) {
  if (arrNumbers[i] + arrNumbers[j] == sum) {
   System.out.println("(" + arrNumbers[i] + "," + arrNumbers[j] + ")");
  }
 }
}
.

9.Check 2nd List has all elements in 1st List
Input

2 List of Elements
{1,2,3,4}{2,3}
{1,2,3,4}{2,5}
{2,3}{2,5,6}  
{2,3}{2,3,9}  

Output

{1,2,3,4}{2,3}  -> true
{1,2,3,4}{2,5}  -> false
{2,3}{2,5,6}    -> false
{2,3}{2,3,9}    -> false

public boolean checkEquals()
{
  Integer orig[] = {1,2,3,4};
  Integer act[] = {2,3};
           
  List origList = new ArrayList(Arrays.asList(orig));
  List actList = Arrays.asList(act);
   
  origList.retainAll(actList);
  System.out.println(origList);
      
  if(actList.size()==origList.size())   
    return true;
  else
    return false; 
}

10.How to find String is anagram?
Output

Keep and Peek are anagrams
silent and listen are anagrams
MotherInLaw and HitlerWoman are anagrams

public class AnagramString 
{
 static void isAnagram(String str1, String str2) 
 {
  String s1 = str1.replaceAll("\\s", "");
  String s2 = str2.replaceAll("\\s", "");
  boolean status = true;

  if (s1.length() != s2.length()) 
   status = false;
  else 
  {
   char[] ArrayS1 = s1.toLowerCase().toCharArray();
   char[] ArrayS2 = s2.toLowerCase().toCharArray();
   Arrays.sort(ArrayS1);
   Arrays.sort(ArrayS2);
   status = Arrays.equals(ArrayS1, ArrayS2);
  }

  if (status)
   System.out.println(s1 + " and " + s2 + " are anagrams");
  else
   System.out.println(s1 + " and " + s2 + " are not anagrams");  
 }

 public static void main(String[] args) 
 {
  isAnagram("Keep", "Peek");
  isAnagram("silent", "listen");
  isAnagram("Mother In Law", "Hitler Woman");
 }
}

11.Check Palindrome
Input

malayalam

Output

Entered string is a palindrome

 public static void main(String args[])
 {
      String original, reverse = "";
      original = "madam";
 
      int length = original.length();
 
      for ( int i = length - 1; i >= 0; i-- )
         reverse = reverse + original.charAt(i);
 
      if (original.equals(reverse))
         System.out.println("Entered string is a palindrome.");
      else
         System.out.println("Entered string is not a palindrome."); 
  }

12.Reverse of String without for loop and array
Input

mugil

Output

ligum

static String reverseMe(String s) 
{
   if(s.length() <= 1)
     return s;

   return s.charAt(s.length() - 1) + reverseMe(s.substring(0,s.length()-1));
 }

13.Check palindrome using recursion
Input

malayalam

Output

palindrome

Call the above reverse function and check with string equals method

public static boolean isPalindrome(String input) 
{
 if (input == null)
  return false;

 String reversed = reverse(input);
 return input.equals(reversed);
}

public static String reverse(String str) 
{ 
 if (str == null) 
  return null;
 
 if (str.length() <= 1) 
  return str;
 
 return reverse(str.substring(1)) + str.charAt(0);
}