门牌制作

门牌制作 - 蓝桥云课 (lanqiao.cn)

思路：

1. 暴力枚举
2. 数位拆分

public class N592 {
	static int[] counts = new int[10];
	public static void main(String[] args) {
		for (int i = 1; i <= 2020; i++) {
			f(i);
		}
		System.out.println(counts[2]);
	}
	private static void f(int num) {
		while (num != 0) {
			counts[num % 10]++;
			num /= 10;
		}
	}
}