Construct a regular expression that recognizes the following language of strings over the alphabet {0 1}:
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Answer:
Here is the JAVA program:
import java.io.*;
import java.util.*;
public class Main {
public static void main(String[] args) throws FileNotFoundException{ //the start of main() function body, it throws an exception that indicates a failed attempt to open the file
Scanner input = new Scanner(new File("file.txt")); //creates a Scanner object and a File object to open and scan through the file.txt
coinFlip(input); } //calls coinFlip method
public static void coinFlip(Scanner input) { //coinFlip method that accepts as its parameter a string input holding a file name
while(input.hasNextLine()) { //iterates through the input file checking if there is another line in the input file
Scanner scan = new Scanner(input.nextLine()); //creates a Scanner object
int head = 0; // stores count of number of heads
int count = 0; //stores count of total number of tokens
while(scan.hasNext()) { //iterates through the sequence checking if there is another sequence in the input file
String token= scan.next(); // checks and returns the next token
if (token.equalsIgnoreCase("H")||token.equalsIgnoreCase("Heads")) { //compares H or Heads with the tokens in file ignoring lower case and upper case differences
head++; } //if a token i.e. any form of heads in file matches with the H or Heads then add 1 to the number of heads
count++; } //increment to 1 to compute total number of counts
double result = Percentage(head, count); //calls Percentage method passing number of heads and total counts to compute the percentage of heads
System.out.println(head + " heads " + "(" + result +"%)"); // prints the number of heads
if(result >= 50.00) { //if the percentage is greater or equal to 50
System.out.println("You win!");} //displays this message if above if condition is true
else //if the percentage is less than 50
{System.out.println("You lose!");} } } //displays this message if above if condition is false
public static double Percentage(int h, int total) { //method to compute the percentage of heads
double p = (double)h/total* 100; // divide number of heads with the total count and multiply the result by 100 to compute percentage
return p; } } //returns result
Explanation:
The program is well explained in the comments mentioned with each line of the above code. I will explain how the method coinFlip works.
Method coinFlip accepts a string holding a file name as its parameter. It opens that file and reads its contents as a sequence of tokens. Then it reads and scans through each token and the if condition statement:
if (token.equalsIgnoreCase("H")||token.equalsIgnoreCase("Heads"))
checks if the each token in the sequence stored in the file is equal to the H or Heads regardless of the case of the token. For example if the first token in the sequence is H then this if condition evaluates to true. Then the head++ statement increments the count of head by 1. After scanning each token in the sequence the variable count is also increased to 1.
If the token of the sequence is HeAds then this if condition evaluates to true because the lower or upper case difference is ignored due to equalsIgnoreCase method. Each time a head is found in the sequence the variable head is incremented to 1.
However if the token in the sequence is Tails then this if condition evaluates to false. Then the value of head variable is not incremented to 1. Next the count variable is incremented to 1 because this variable value is always incremented to 1 each time a token is scanned because count returns the total number of tokens and head returns total number of heads in the tokens.
Percentage method is used to return the percentage of the number of heads in the sequence. It takes head and count as parameters (h and total). Computes the percentage by this formula h/total* 100. If the result of this is greater than or equal to 50 then the message You win is displayed otherwise message You lose! is displayed in output.
