题解 | #跳台阶#

#include <iostream>
using namespace std;

int main() {
    int p = 1,q = 2,r = 3;//定义三个变量进行输出，将时间复杂度将至O(n)
    int res;
    cin>>res;
    if(res == 1){
        cout<<1;
        return 0;
    }
    if(res == 2){
        cout<<2;
        return 0;
    }
    for(int i=4;i<=res;i++){
        p = q;
        q = r;
        r = p+q;
    }
    cout<<r;
    return 0;
 }