题解 | 跳台阶扩展问题

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        if (num <= 2) {
            System.out.println(num);
            return;
        }
        int[] arr = new int[num];
        arr[0] = 1;
        arr[1] = 2;
        for (int i = 2 ; i < num ; i++) {
            for (int j = i - 1; j >= 0; j--) {
                arr[i] += arr[j];
            }
            arr[i] += 1;
        }
        System.out.println(arr[num - 1]);

    }
}