Fibonacci

求斐波纳契数列第n个数的两种实现方法。

public class TestFibo {
    
    public static void main(String[] args){
        System.out.println(f(7));
        System.out.println(fn(7));
    }
    
    //递归实现
    public static  long f(int index){
        
        if(index<1){
            System.out.println("wrong number");
            return (long)0;
        }else if(index==1||index==2){
            return (long)1;
        }else {
            return (f(index-1)+f(index-2));
        }
    }
    
    //非递归实现
    public static long fn(int index){
        
        long f1 = 1l;
        long f2 = 1l;
        long f3 = 0l;
        if(index<1){
            System.out.println("wrong number");
            return (long)(-1);
        }else if(index==1||index==2){
            return (long)f1;
        }else{
            for (int i=0;i<(index-2);i++){
                f3 = f1 + f2;
                f1 = f2;
                f2 = f3;
            }
            
            return f3;
        }
    }

}