The Deaf Rats of Hamelin Problem in Java

The problem

The Pied Piper has been enlisted to play his magical tune and coax all of the rats out of city.

However a number of the rats are deaf and are going the improper means!

Job

What number of deaf rats are there?

Legend

• P = The Pied Piper
• O~ = Rat going left
• ~O = Rat going proper

Examples

• ex1 ~O~O~O~O P has 0 deaf rats
• ex2 P O~ O~ ~O O~ has 1 deaf rat
• ex3 ~O~O~O~OP~O~OO~ has 2 deaf rats

The answer in Java code

Possibility 1:

public class DeafRatsOfHamelin {
    public static int countDeafRats(remaining String city) {
        String t = city.replaceAll(" ","");
        int rely = 0;
        for (int i = 0 ; i < t.size() ; i+=2) if (t.charAt(i) == 'O') rely++;
        return rely;
    }
}

Possibility 2:

import java.util.stream.IntStream;

public class DeafRatsOfHamelin {
  public static int countDeafRats(remaining String city) {
    remaining String s = city.replaceAll("s+", "");
    return (int) IntStream.vary(0, s.size()).filter(i -> s.charAt(i) == '~' && ipercent2 > 0).rely();
  }
}

Possibility 3:

public class DeafRatsOfHamelin {
  public static int countDeafRats(remaining String city) {
    int DeafRats=0;   
    String CompactTown;   
    CompactTown = city.change(" ","");
    for(int i=0;i<CompactTown.size();i+=2){   
        if(CompactTown.charAt(i) == 'O') DeafRats++;     
    }
    return DeafRats;
  }
}

Check circumstances to validate our resolution

import org.junit.jupiter.api.Check;
import static org.junit.jupiter.api.Assertions.*;

class DeafRatsOfHamelinTest {
    @Check
    public void ex1() {
        assertEquals(0, DeafRatsOfHamelin.countDeafRats("~O~O~O~O P"));
    }
    @Check
    public void ex2() {
        assertEquals(1, DeafRatsOfHamelin.countDeafRats("P O~ O~ ~O O~"));
    }
    @Check
    public void ex3() {
        assertEquals(2, DeafRatsOfHamelin.countDeafRats("~O~O~O~OP~O~OO~"));
    }
}

Further take a look at circumstances

import org.junit.Check;
import static org.junit.Assert.assertEquals;

public class SolutionTests {
  @Check
  public void ex1() {
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("~O~O~O~O P"));
  }
  
  @Check
  public void ex2() {
    assertEquals(1, DeafRatsOfHamelin.countDeafRats("P O~ O~ ~O O~"));
  }
  
  @Check
  public void ex3() {
    assertEquals(2, DeafRatsOfHamelin.countDeafRats("~O~O~O~OP~O~OO~"));
  }

  @Check
  public void rats() {
    assertEquals(8, DeafRatsOfHamelin.countDeafRats("O~~OO~~OO~~OO~P~OO~~OO~~OO~~O"));
    assertEquals(8, DeafRatsOfHamelin.countDeafRats("O~~OO~~OO~~OO~ P~OO~~OO~~OO~~O"));
    assertEquals(8, DeafRatsOfHamelin.countDeafRats("O~~OO~~OO~~OO~P ~OO~~OO~~OO~~O"));
  }
  
  @Check
  public void highlander() {
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("~OP"));
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("PO~"));
    assertEquals(1, DeafRatsOfHamelin.countDeafRats("O~P"));
    assertEquals(1, DeafRatsOfHamelin.countDeafRats("P~O"));
  }

  @Check
  public void empty() {
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("         P"));
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("P         "));
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("         P      "));
    assertEquals(0, DeafRatsOfHamelin.countDeafRats("P"));
  }

  // ====================================
  
  // Reference implementation for the Random take a look at circumstances
  non-public static class DeafRatsOfHamelin {
  
    static int countDeafRats(remaining String city) {
      String s = "";
      for (int i = 0; i < city.size(); i++) {
        remaining char c = city.charAt(i);
        if (c == '~') { s += "R"; i ++; }
        else if (c == 'O') { s += "L"; i ++; }
        else if (c == 'P') { s += c; }
      }
      remaining String s1 = s.substring(0, s.indexOf("P")), s2 = s.substring(s.indexOf("P")+1);
      int deaf = 0;
      // Rats to left of the Piper must be going proper
      deaf += s1.change("R","").size();
      // Rats to proper of the Piper must be going left
      deaf += s2.change("L","").size();
      return deaf;
    }
  
  }
  
  non-public static String makeRatFacing(remaining char principally) {
    remaining double d = Math.random() * 3;
    if (principally == 'L') {
      // Largely dealing with left
      if (d < 2.5) return "O~";
      if (d < 2.8) return "~O";
    } else {
      // Largely dealing with proper
      if (d < 2.5) return "~O";
      if (d < 2.8) return "O~";
    }
    return "  ";
  }
  
  non-public static String makeTown(char piperPos) {
    remaining int ratsLeft = (int)(Math.random() * 20) + 5;
    remaining int ratsRight = (int)(Math.random() * 20) + 5;
    String city = "";
    boolean piper = false;
    if (piperPos == 'L') { city += "P"; piper = true; }
    for (int r = 0; r < ratsLeft; r++) {
      city += makeRatFacing(piper ? 'L' : 'R');
    }
    if (piperPos == 'M') { city += "P"; piper = true; }
    for (int r = 0; r < ratsRight; r++) {
      city += makeRatFacing(piper ? 'L' : 'R');
    }
    if (piperPos == 'R') city += "P";
    return city;
  }
  
  @Check
  public void random() {
    for (int r = 1; r <= 200; r++) {
      remaining int p = (int)(Math.random() * 3);
      remaining char piper = p == 0 ? 'L' : p == 1 ? 'M' : 'R';
      remaining String city = makeTown(piper);
      remaining int anticipated = DeafRatsOfHamelin.countDeafRats(city);
      System.out.println(String.format("Random take a look at %d : <span type='shade:inexperienced'>%s</span> has %d deaf rats", r, city, anticipated));      
      assertEquals(anticipated, DeafRatsOfHamelin.countDeafRats(city));
    }
  }
}