爬楼梯

package day01;

import java.util.Scanner;

public class climbStairs {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner print = new Scanner(System.in );
        System.out.print("请给楼梯阶数n赋值：");
        int n =print.nextInt();
        climbStairs(n);
//        int a=climbStairs(5);
//        System.out.println(a);
// 
    }
    public static int climbStairs(int n) {
        // write your code here
        if(n == 0) {
            System.out.println("阶数为0，不存在爬楼梯步数");
            return -1;
            }
        if(n <= 2){
            System.out.println("当阶数为1或2时，爬楼梯步数即为1或2");
            return n;
        }
        int n1=1,n2=2,n3=0;
        for(int i = 3; i <= n; i++)
            {
                 n3 = n1 + n2;
                 n1=n2 ;
                 n2 = n3;
            }
        System.out.println("阶数为"+n+"时的爬楼梯数为："+n3);
        return n3;
    }

}