Fibonacci.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

/**
 *
 * @author Varun Upadhyay (https://github.com/varunu28)
 *
 */

public class Fibonacci {

 private static Map<Integer,Integer> map = new HashMap<Integer,Integer>();

 public static void main(String[] args) throws Exception {

 BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 int n = Integer.parseInt(br.readLine());

 System.out.println(fibMemo(n)); // Returns 8 for n = 6
 System.out.println(fibBotUp(n)); // Returns 8 for n = 6
 }

 /**
 * This method finds the nth fibonacci number using memoization technique
 *
 * @param n The input n for which we have to determine the fibonacci number
 * Outputs the nth fibonacci number
 **/

 private static int fibMemo(int n) {
 if (map.containsKey(n)) {
 return map.get(n);
 }

 int f;

 if (n <= 2) {
 f = 1;
 }
 else {
 f = fibMemo(n-1) + fibMemo(n-2);
 map.put(n,f);
 }

 return f;
 }

 /**
 * This method finds the nth fibonacci number using bottom up
 *
 * @param n The input n for which we have to determine the fibonacci number
 * Outputs the nth fibonacci number
 **/

 private static int fibBotUp(int n) {

 Map<Integer,Integer> fib = new HashMap<Integer,Integer>();

 for (int i=1;i<n+1;i++) {
 int f = 1;
 if (i<=2) {
 f = 1;
 }
 else {
 f = fib.get(i-1) + fib.get(i-2);
 }
 fib.put(i, f);
 }

 return fib.get(n);
 }
}