斐波那契数列解法及其优化解法

使用非递归解法复杂度更低

/**
 * 斐波那契数列
 * @author DUSTDAWN
 *
 */
public class Solution_6 {
	public static void main(String[] args) {
		System.out.println(Fibonacci(-10));
		System.out.println(FiBest(-10));
	}
	/**
	 * 时间复杂度O(2^n)
	 * @param n
	 * @return
	 */
	public static int Fibonacci(int n) {
		if(n<0) 
			return 0;
		if(n==1)
			return 1;
		return Fibonacci(n-1)+Fibonacci(n-2);
	}
	/**
	 * 时间复杂度O(n)
	 * @param n
	 * @return
	 */
	public static int FiBest(int n) {
		int result[] = {0,1};
		try {
			if(n<2) 
				return result[n];
		}catch(Exception e) {return 0;}
		
		int Fi_one = 0;
		int Fi_two = 1;
		int Fi_n = 0;
		for(int i = 1;i<n;i++) {
			Fi_n = Fi_one + Fi_two; 
			Fi_one = Fi_two;
			Fi_two = Fi_n;
		}
		
		return Fi_n;
	}
}