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;
}
}
}
