[leedcode 70] Climbing Stairs

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?

public class Solution {
public int climbStairs(int n) {
//f(n)=f(n-1)+f(n-2);DP

int f1=1;
int f2=2;
/*for(int i=3;i<=n;i=i+2){
f1=f1+f2;
f2=f1+f2;
}
if(n%2==0) return f2;
else return f1;*/
// 解法二：
if(n==1) return 1;
if(n==2) return 2;
for(int i=3;i<=n;i++){
int f3=f1+f2;
f1=f2;
f2=f3;

}
return f2;
}
}