convertingNumber

ConvertNumberToRoman

private static String RomanNumerals(int value){
		
    LinkedHashMap<String, Integer> roman_numerals = new LinkedHashMap<String,Integer>();
    roman_numerals.put("M", 1000);
    roman_numerals.put("CM", 900);
    roman_numerals.put("D", 500);
    roman_numerals.put("CD", 400);
    roman_numerals.put("C", 100);
    roman_numerals.put("XC", 90);
    roman_numerals.put("L", 50);
    roman_numerals.put("XL", 40);
    roman_numerals.put("X", 10);
    roman_numerals.put("IX", 9);
    roman_numerals.put("V", 5);
    roman_numerals.put("IV", 4);
    roman_numerals.put("I", 1);
    String res = "";
    
    for (Map.Entry<String, Integer> entry : roman_numerals.entrySet()){
    	int matches = value/entry.getValue();
        res += repeat(entry.getKey(), matches);
        value = value % entry.getValue();
    }
	
	return res;
}

public static String repeat(String s, int n){
	if(s == null) {
        return null;
    }
    final StringBuilder sb = new StringBuilder();
    for(int i = 0; i < n; i++) {
        sb.append(s);
    }
    return sb.toString();
}

ConvertNumberToWord

private static final String[] lowNames = {
   "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten",
   "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"};

private static final String[] tensNames = {
   "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"};

private static final String[] bigNames = {
   "thousand", "million", "billion"};

/**
* Converts an integer number into words (american english).
* @author Christian d'Heureuse, Inventec Informatik AG, Switzerland, www.source-code.biz
**/
public String convertNumberToWord (int n) {
   if (n < 0) {
      return "minus " + convertNumberToWord(-n); }
   if (n <= 999) {
      return convert999(n); }
   String s = null;
   int t = 0;
   while (n > 0) {
      if (n % 1000 != 0) {
         String s2 = convert999(n % 1000);
         if (t > 0) {
            s2 = s2 + " " + bigNames[t-1]; }
         if (s == null) {
            s = s2; }
          else {
            s = s2 + ", " + s; }}
      n /= 1000;
      t++; }
   return s; }

// Range 0 to 999.
private static String convert999 (int n) {
   String s1 = lowNames[n / 100] + " hundred";
   String s2 = convert99(n % 100);
   if (n <= 99) {
      return s2; }
    else if (n % 100 == 0) {
      return s1; }
    else {
      return s1 + " " + s2; }
}

// Range 0 to 99.
private static String convert99 (int n) {
   if (n < 20) {
      return lowNames[n]; }
   String s = tensNames[n / 10 - 2];
   if (n % 10 == 0) {
      return s; }
   return s + "-" + lowNames[n % 10]; 
}

fibonacci

public static void main(String[] args) {

		for(int i=1;i<=10;i++){
			//cara 1:
//			System.err.print(getNumberFibonacci(i)+" ");
			//cara 2:
			System.out.print(fibonacciRecursion(i)+" ");
		}
		
	}
	
	private static int fibonacciRecursion(int n){
		if(n == 1 || n==2){
			return 1;
		}
		return fibonacciRecursion(n-1)+fibonacciRecursion(n-2);
	}
	
	private static int getNumberFibonacci(int number){
		if(number == 1 || number==2){
			return 1;
		}
		int numberOf = 1, lastNumber = 1, beforeNumber = 1;
		for(int i=3;i<=number;i++){
			numberOf = beforeNumber + lastNumber;
			beforeNumber = lastNumber;
			lastNumber = numberOf;
		}
		
		return numberOf;
	}
	
	//if fibonacci begin in first number is bil1 and second number bil2. 
	private static int fibo(int bil1, int bil2, int x){
		if(x==1)
			return bil1;
		if(x==2)
			return bil2;
		return fibo(bil1, bil2, x-1)+fibo(bil1, bil2, x-2);
	}

polindrome

private static boolean polindrome(String in){
	if(in == null) 
		return false;
	StringBuilder strBuild = new StringBuilder(in);
	strBuild.reverse();
	System.out.println(in +" <> "+strBuild);
	System.out.println(in.compareTo("popa"));
	return strBuild.toString().equals(in);
}