jz009

#####青蛙一次可以跳1，2，3***，n个台阶，问有多少种跳法
public static int test1(int n){
    int res=0;
    if (n<=3){
        for (int i=0;i<=n;i++){
            res+=i;
        }
        return res;
    }
    res=6;
    int i=3;
    int start =2;
    int end =3;
    int zc;
    while (i<n){
        zc=start+end;
        res+=zc;
        start=end;
        end=zc;
        i++;
    }
    return res;
}