HELP IN JAVA: *NOTE: contents of input file will put in the bottom Write a progr

Question

HELP IN JAVA: *NOTE: contents of input file will put in the bottom

Write a program to read several lines from a file. For each line, check whether it is a palindrome or nearly a palindrome. For each line read from the file, print only the lines that are palindromes or nearly palindromes. Recall that a palindrome is a number that is the same backwards and forwards. Some examples of palindromes are 14641 and 22. A number that is nearly a palindrome is a number where if you changed 1 digit, it would be a palindrome. Some examples are 14671 and 32. Your palindrome checking method must be recursive.

You need a recursive method that checks to see if a number is a palindrome or nearly a palindrome. Some hints:

1. This is actually easiest if you convert the number to a string and then check the characters of the string.

2. You need to check the characters of the string from the left and from the right simultaneously to see if they match.

3. The check is allowed 1 mismatch, but only 1—no more.

4. You can keep track of everything in parameters in the recursive method: the string, the left position, the right position, and the number of mismatches found so far. So the recursive method header looks like this: boolean detectPalindrome(String s, int left, int right, int mismatches)

5. When you call the method the first time, there are 0 mismatches, left starts at position 0, and right at the last character of the string. So the initial method call looks like this: detectPalindrome(s, 0, s.length()-1, 0)

6. Now, there are two stopping cases (base cases): The first is when the check hits two mismatches. At that point you know the number is not a palindrome or nearly a palindrome, so you can return false: if (mismatches==2) return false;

7. The other stopping case is when the check hits the middle of string and there are less than 2 mismatches. The middle of the string is either when left and right hit the single digit in the middle (for an odd-length string) or they cross over each other because all the digits have been checked (for an even-length string). You can check this with one expression like this: if (right-left <= 0) return true;

8. Finally, there are two recursive cases: one where there is a match and one where there is a mismatch. In the second case, you have to add 1 to the number of mismatches in the recursive call. In both cases you have to add 1 to the left position and subtract one from the right position: if (s.charAt(left)==s.charAt(right)) return detectPalindrome(s, left+1, right-1, mismatches); else return detectPalindrome(s, left+1, right-1, mismatches+1);

9. That is all you need for the recursive method. The last thing to do is combine this with reading numbers from the file.

*palinTest.txt*

6171

81513111

316111

69396

6101

122221

313161

61514161

11310161

7161

61813111

61212111

31013171

312101

41313121

61515151

811141

2151

56365

717101

5151

12

3171

213131

51515131

33

2141

611171

384463

61813181

8131

21814141

66

11612151

114131

71214181

71511101

318101

81110131

96

514181

99

41818141

11016151

61510151

58382

25352

616121

71414121

5141

418141

21516111

61813131

8141

5131

71817161

512131

81117131

115101

238232

416181

61518131

23332

413101

5121

117131

81116111

24442

21810121

115161

7161

311171

21115131

81118101

31317131

6151

2161

31811141

198891

218111

21017151

816151

81415121

711101

816151

4181

21312

11216181

3141

118141

56375

81211131

41515141

19

4101

49394

61016111

614171

41364

61514121

414161

216111

538838

617181

31311131

939969

8131

110161

3121

2101

6121

Explanation / Answer

PROGRAM

import java.io.*;

// Create PalTest class
class PalTest
{
// create and implement static method detectPalindrome() method
public static boolean detectPalindrome(String s,int left,int right,int mismatches)
{
if(mismatches==2) return false; // check condition mismatches=2 then return false
if(mismatches<2){ // check condition mismatches<2 then right-left<=0 then return true
if ((right-left) <= 0) return true;
}

if(s.charAt(left)==s.charAt(right)) // check condition left digit and right digits are equal then
return detectPalindrome(s,left+1,right-1,mismatches); // call recursively the parameter mismatches=0
else
return detectPalindrome(s,left+1,right-1,mismatches+1); // else call recursively the add 1 to parameter mismatches

}

public static void main(String [] args) throws IOException
{
try // open try..catch block to check whether the file is available or not
{
File f=new File("F:\palinTest.txt"); // create object f for File
BufferedReader b=new BufferedReader(new FileReader(f)); // create object b of BufferedReader
String str=""; // initialized String str null
  
while((str=b.readLine())!=null){ // create while loop until end-of-file
  
if(detectPalindrome(str,0,str.length()-1,0)) // calling detectPalindrome and check condition then display palindrome else not palindrome
System.out.println("Palindrome= "+str);
else
System.out.println("Not Palindrom= "+str);
}
}catch(IOException e) // catch, when the file is not found, then display IOException
{
e.printStackTrace();
}
}
}

OUTPUT

F:>javac PalTest.java

F:>java PalTest
Not Palindrom= 6171
Not Palindrom= 81513111
Not Palindrom= 316111
Palindrome= 69396
Not Palindrom= 6101
Palindrome= 122221
Not Palindrom= 313161
Not Palindrom= 61514161
Not Palindrom= 11310161
Not Palindrom= 7161
Not Palindrom= 61813111
Not Palindrom= 61212111
Not Palindrom= 31013171
Not Palindrom= 312101
Not Palindrom= 41313121
Not Palindrom= 61515151
Not Palindrom= 811141
Not Palindrom= 2151
Palindrome= 56365
Not Palindrom= 717101
Not Palindrom= 5151
Palindrome= 12
Not Palindrom= 3171
Not Palindrom= 213131
Not Palindrom= 51515131
Palindrome= 33
Not Palindrom= 2141
Not Palindrom= 611171
Palindrome= 384463
Not Palindrom= 61813181
Not Palindrom= 8131
Not Palindrom= 21814141
Palindrome= 66
Not Palindrom= 11612151
Not Palindrom= 114131
Not Palindrom= 71214181
Not Palindrom= 71511101
Not Palindrom= 318101
Not Palindrom= 81110131
Palindrome= 96
Not Palindrom= 514181
Palindrome= 99
Not Palindrom= 41818141
Not Palindrom= 11016151
Not Palindrom= 61510151
Palindrome= 58382
Palindrome= 25352
Not Palindrom= 616121
Not Palindrom= 71414121
Not Palindrom= 5141
Not Palindrom= 418141
Not Palindrom= 21516111
Not Palindrom= 61813131
Not Palindrom= 8141
Not Palindrom= 5131
Not Palindrom= 71817161
Not Palindrom= 512131
Not Palindrom= 81117131
Not Palindrom= 115101
Palindrome= 238232
Not Palindrom= 416181
Not Palindrom= 61518131
Palindrome= 23332
Not Palindrom= 413101
Not Palindrom= 5121
Not Palindrom= 117131
Not Palindrom= 81116111
Palindrome= 24442
Not Palindrom= 21810121
Not Palindrom= 115161
Not Palindrom= 7161
Not Palindrom= 311171
Not Palindrom= 21115131
Not Palindrom= 81118101
Not Palindrom= 31317131
Not Palindrom= 6151
Not Palindrom= 2161
Not Palindrom= 31811141
Palindrome= 198891
Not Palindrom= 218111
Not Palindrom= 21017151
Not Palindrom= 816151
Not Palindrom= 81415121
Not Palindrom= 711101
Not Palindrom= 816151
Not Palindrom= 4181
Palindrome= 21312
Not Palindrom= 11216181
Not Palindrom= 3141
Not Palindrom= 118141
Palindrome= 56375
Not Palindrom= 81211131
Not Palindrom= 41515141
Palindrome= 19
Not Palindrom= 4101
Palindrome= 49394
Not Palindrom= 61016111
Palindrome= 14171
Not Palindrom= 1364
Palindrome= 1514121
Palindrome= 14161
Not Palindrom= 216111
Palindrome= 538838
Not Palindrom= 617181
Not Palindrom= 31311131
Palindrome= 939969
Not Palindrom= 8131
Not Palindrom= 110161
Not Palindrom= 3121
Not Palindrom= 2101
Not Palindrom= 6121
Palindrome= 14671
Palindrome= 32

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