Generate Combination in java

public class Combination {

     void doCombination(char []str,int start,int end){   

     char []data=new char[3];

     int i=0;

     int r=3;// how many element combine in one selection

     doCombinationUntil(str,data,start,end,i,r);

     }

    

   void   doCombinationUntil(char []str,char []data,int start,int end,int index,int r){

        if (index==r) {

          for (int j = 0; j < r; j++) {

              System.out.print(data[j]);

          }

          System.out.println("");

          return;

     }

        for (int i=start; i<=end && end-i+1 >= r-index; i++)

         {

             data[index] = str[i];

             doCombinationUntil(str, data, i+1, end, index+1, r);

         }

     }

    

     public static void main(String[] args) {  

          String str1="abcd";

          char []str=str1.toCharArray();

          Combination obj=new Combination();

          obj.doCombination(str,0,(str.length-1));

     }

    

}

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Generate permutation of string

Permutation:

each of several possible ways in which a set or number of things can be ordered or arranged. 

public class permutation {

  void    doPermutation(char [] str,int i,int n){

       if (i==n) {

          for (int m = 0; m < str.length; m++) {

       System.out.print(str[m]);

          }

          System.out.println("");

    

     }

       else{

            for (int j = i; j <=n; j++) {

                //swap str[i] and str[j]

                 char ch=str[i];

                 str[i]=str[j];

                 str[j]=ch;

                 doPermutation(str, i+1, n);

                 //swap str[i] and str[j]

                 ch=str[i];

                 str[i]=str[j];

                 str[j]=ch;

          }

       }

         

     }   

     public static void main(String[] args) {

    

          String str1="abc";

          permutation obj=new permutation();

          char []str=str1.toCharArray();

          obj.doPermutation(str,0,(str.length-1));       

     }

    

}

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Dynamic array in java

When we enter element in array but array is full then create a function, this function create a new array double size and copy element from previous array to new array  and return this new array 

public class DynamicArray {

 static   int []increaseSizeOfArray(int []arr){

          int []brr=new int[(arr.length*2)];

          for (int i = 0; i < arr.length; i++) {

         brr[i]=arr[i];     

          }

          return brr;

     }

public static void main(String[] args) {

     int []arr=new int[5];

      for (int i = 0; i < 11; i++) {

          if (i<arr.length) {

              arr[i]=i+100;

          }

          else {

              arr=increaseSizeOfArray(arr);

              arr[i]=i+100;

          }        

     }

      

for (int i = 0; i < arr.length; i++) {

     System.out.println("arr="+arr[i]);

}   

}

}

How to generate random number in java

Here we learn how to generate random number in java

public class RandomNumber {

public static void main(String[] args) {

    

     int c;

    Random t = new Random();

    // random integers in [0, 100]

    for (c = 1; c <= 10; c++) {

      System.out.println(t.nextInt(100));

    }

}

} 

Find absolute value of any number

the absolute value (or modulus) |x| of a real number x is the non-negative value of x without regard to its sign.

If number is less than zero return -(number) otherwise return number

public class OwnAbsoluteFunction {

   

     static int getAbsolute(int i){

          return(i>0?i:-i);

     }

    

     public static void main(String[] args) {

          int i=-10;

        System.out.println("i="+getAbsolute(i));

     }

    

}

   

Reverse string in java

 Reverse string in java
public class reverse_string {
   
    public static void main(String[] args) {
        String str="nit kurukshetra is a good college in india";
        char arr[]=str.toCharArray();
        int j=arr.length-1;
        int i=0;
        while(i<j){
            char ch=arr[i];
            arr[i]=arr[j];
            arr[j]=ch;
        i++;
        j--;
        }
     for (int k = 0; k < arr.length; k++) {
        System.out.print(arr[k]);   
    }  
       
    }

}

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Find duplicate charcters with occurrences in a string

 A string contain some duplicate characters.find duplicate charcter with occurrences
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("javatipsall");
    }
}
=============================
Output:
a--->3
l--->2

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Reverse string in java (Solution).

Find duplicate characters with occurrences in a string(Solution).

Permutation of a number(Soluion).

Split the String in java(Solution).

Convert string into number in java(Solution).

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Expand String(Solution).

Reverse String (Solution).