【Codeforces】1213C – Book Reading
Problem Description:
Polycarp is reading a book consisting of n pages numbered from 1 to n. Every time he finishes the page with the number divisible by m, he writes down the last digit of this page number. For example, if n=15 and m=5, pages divisible by m are 5,10,15. Their last digits are 5,0,5 correspondingly, their sum is 10.
Your task is to calculate the sum of all digits Polycarp has written down.
You have to answer q independent queries.
Input Specification:
The first line of the input contains one integer q (1 ≤ q ≤ 1000) — the number of queries.
The following q lines contain queries, one per line. Each query is given as two integers n and m (1 ≤ n,m ≤
Output Specification:
For each query print the answer for it — the sum of digits written down by Polycarp.
Sample Input:
7
1 1
10 1
100 3
1024 14
998244353 1337
123 144
1234312817382646 13
Sample Output:
1
45
153
294
3359835
427262129093995
解题思路:
这道题目的大意是在[1, n]这个区间内,若存在某个数 i 是m的倍数,则把 i 的个位数加起来的和sum进行输出。我一开始的想法就是暴力破解就完事啦,毫无疑问地直接TLE了。没点办法 只能开动我的小脑筋啦。先把所有能整除m的数的个位数列出来,然后计算一共有多少个数会出现以这个尾数结尾的情况,用sum += cnt*d(表示有cnt个以d为个位数且能整除m的数),最后将sum进行输出即可。
AC代码:TLE代码:
AC代码:

原文链接:【Codeforces】1213C - Book Reading
麦芽雪冷萃 版权所有,转载请注明出处。
还没有任何评论,你来说两句吧!