8662 234的和

⭐️难度：中等
🌟考点：模拟、二维前缀和
📖

📚

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {
    static int[] a = new int[15];
    static long[][] dp = new long[15][100];

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int l = sc.nextInt();
        int r = sc.nextInt();
        for(long x[] : dp){
            Arrays.fill(x,-1);
        }
        System.out.println(f(r) - f(l - 1));
    }

    static long f(int x){
        int cnt = 0;
        while(x != 0){
            a[++cnt] = x % 10;
            x /= 10;
        }
        return  dfs(true,cnt,0);
    }

    static long dfs(boolean lim,int pos,int sum){
        if(pos == 0) return sum;
        if(dp[pos][sum] != -1 && !lim) return dp[pos][sum]; // !lim
        int up = lim ? a[pos] : 9;
        long res = 0;
        for(int i = 0;i <= up;i++){
            if(i == 2 || i == 3 || i == 4){
                res = res + dfs(lim && i == up,pos - 1,sum + i); // lim && i == up
            }else{
                res = res + dfs(lim && i == up,pos - 1,sum); // lim && i == up
            }
        }
        if(!lim) dp[pos][sum] = res;
        return res;
    }
}

🍎笔记