You are climbing a stair case. It takes n steps to reach to the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
简单递推
class Solution {
public:
int climbStairs(int n) {
long long ans=0;
if(n==1) return 1;
if(n==2) return 2;
int a=1,b=2;
n-=2;
while(n--){
ans=a+b;
a=b;
b=ans;
}
return ans;
}
};