Day8 剑指offer：青蛙跳台阶

一只青蛙一次可以跳上1级台阶，也可以跳上2级。求该青蛙跳上一个n级的台阶总共有多少种跳法。

public class Solution {
    public int JumpFloor(int target) {
        if(target == 1) return 1;
        else if(target == 2) return 2;
        else return JumpFloor(target-1) + JumpFloor(target-2);
    }
}

public class Solution {
    public int JumpFloor(int target) {
        if(target == 1) return 1;
        else if(target == 2) return 2;
        else{
            int res = 0;
            int a = 1;
            int b = 2;
            for(int i=3; i<=target; i++){
                res = a + b;
                a = b;
                b = res;
            }
            return res;
        }

    }
}