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Reverse, add and check for palindrome
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.math.BigInteger;
/**
* Created by IntelliJ IDEA.
*
* @author: ramswaroop
* @date: 9/16/15
* @time: 10:53 PM
*/
public class ReverseAndAdd {
/**
* Reverses the number {@param n}.
*
* @param n
* @return the reverse of the number {@param n}.
*/
public static BigInteger getReverse(BigInteger n) {
return new BigInteger(new StringBuilder().append(n).reverse().toString());
}
/**
* Checks if {@param n} is palindrome.
*
* @param n
* @return {@code true} if {@param n} is palindrome.
*/
public static boolean isPalindrome(BigInteger n) {
return n.compareTo(getReverse(n)) == 0;
}
/**
* Checks if {@param n} is negative.
*
* @param n
* @return {@code true} if {@param n} is negative, {@code false} otherwise.
*/
public static boolean isNegative(BigInteger n) {
return n.compareTo(new BigInteger("0")) == -1;
}
/**
* Reverses the number {@param n}, adds to itself and then checks
* for palindrome.
*
* @param n
* @return an array of {@code BigInteger} with number of additions and final palindrome number respectively.
*/
public static BigInteger[] reverseAddAndCheck(String n) {
BigInteger additions = new BigInteger("1");
BigInteger original = new BigInteger(n);
boolean isNegative = isNegative(original);
if (isNegative) original = original.multiply(new BigInteger("-1"));
BigInteger reverse;
while (!isPalindrome(original.add(reverse = getReverse(original)))) {
original = original.add(reverse);
additions = additions.add(new BigInteger("1"));
}
original = original.add(reverse);
if (isNegative) original = original.multiply(new BigInteger("-1"));
return new BigInteger[]{additions, original};
}
/**
* Reads the input file mentioned in {@param filePath} line by line
* and calls {@code reverseAddAndCheck()} for every line.
*
* @param filePath
*/
public static void readFile(String filePath) {
try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
String line;
while ((line = br.readLine()) != null) {
BigInteger[] result = reverseAddAndCheck(line);
System.out.println(result[0].toString() + " " + result[1].toString());
}
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Starting point of the program.
*
* @param a
*/
public static void main(String a[]) {
readFile(a[0]);
System.exit(0);
}
}
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