SW练习_ P1255 数楼梯_动态规划

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigDecimal;
import java.util.StringTokenizer;
public class Main {
    public static void main(String[] args) throws Exception{
        BufferedReader reader=new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st=new StringTokenizer(reader.readLine());
        int N=Integer.parseInt(st.nextToken());
        BigDecimal[] arr=new BigDecimal[N+1];
        if(N==0){
            System.out.println(0);
            return;
        }else if(N==1){
            System.out.println(1);
            return;
        }else if(N==2){
            System.out.println(2);
            return;
        }
        arr[1]=new BigDecimal(1);
        arr[2]=new BigDecimal(2);
        for (int i = 3; i <=N ; i++) {
            arr[i]=arr[i-1].add(arr[i-2]);
        }
        System.out.println(arr[N]);

        reader.close();
    }
}