斐波那契数列

package com.yan.offer;

/**
 * 大家都知道斐波那契数列(0、1、1、2、3、5、8、13、21、34 ...)，F(n)=F(n-1)+F(n-2),
 * 现在要求输入一个整数n，请你输出斐波那契数列的第n项。
 * 
 * @author Yan
 *
 */
public class Fibonacci {

    public Fibonacci() {
    }

    public static void main(String[] args) {
        Fibonacci fibonacci = new Fibonacci();
        System.out.println(fibonacci.findNth2(0));
    }

    /*
     * recursive implementation, however the cost is too expensive.
     */
    public int findNth(int n) {

        if (n < 0)
            return -1;
        if (n == 0)
            return 0;
        if (n == 1) {
            return 1;
        }
        return findNth(n - 1) + findNth(n - 2);

    }

    /**
     * An implementation without recurse. It is faster than the recursive
     * implementation.
     * 
     * @param n
     * @return
     */
    public int findNth2(int n) {
        if (n < 0)
            return -1;
        if (n == 0)
            return 0;
        if (n == 1)
            return 1;
        if (n >= 2) {
            /*
             * declare two point (not very exactly) to record F(n-2) and F(n-1)
             * and move step by step.
             */
            int temp1 = 0;
            int temp2 = 1;
            int result = temp1 + temp2;
            for (int i = 2; i <= n; i++) {
                result = temp1 + temp2;
                temp1 = temp2;
                temp2 = result;
            }
            return result;
        }
        return -1;
    }

}