剑指Offer-9

题目：

写一个函数，输入 n ，求斐波那契数列的第n项

实现

public class Solution9 {    //直接递归，，当递归深度较深时，效率很低    public int Fibonacci1(int n){        if(n<0){            throw new RuntimeException("n 小于 0，输入不合法");        }        if(n<2){            return n;        }        return Fibonacci1(n-1)+Fibonacci1(n-2);    }    public int Fibonacci2(int n){        int[] result={0,1};        if(n<0){            throw new RuntimeException("n 小于 0，输入不合法");        }        if(n<2){            return result[n];        }        int fibo_one = 0;        int fibo_two = 1;        int fibo_n=0;        for(int i=2;i<=n;i++){            fibo_n = fibo_one+fibo_two;            fibo_one = fibo_two;            fibo_two = fibo_n;        }        return fibo_n;    }    public static void main(String[] args){        int n = 9;        Solution9 s9 = new Solution9();        int result1 = s9.Fibonacci1(n);        int result2 = s9.Fibonacci2(n);        System.out.println(result1);        System.out.println(result2);    }}