AtCoder Beginner Contest 048 B - Between a and b

Problem Statement

You are given nonnegative integers $a$

and $b$ ($\mathrm{a\le b}$), and a positive integer $x$. Among the integers between $a$ and $b$, inclusive, how many are divisible by $x$

• $\mathrm{1\le x\le 1018}$

$a$ $b$ $x$

and $b$, inclusive, that are divisible by $x$.

易知0到a内整除x的数的个数为a/x+1，所以a不整除x时答案为(b/x-a/x)，在整除时还要再加一。

注意，不要把(b/x-a/x)合并为(b-a)/x，虽然在数学上是对的，但在计算机中除法是下取整的，可能会导致精度不对。例如a=2，b=6，x=3时b/x-a/x=2，但(b-a)/x=1。

下为代码：

 1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 int main()
 5 {
 6     unsigned long long a, b, x, ans;
 7     cin >> a >> b >> x;
 8     if (a > b)
 9     {
10         cout << 0;
11         return 0;
12     }
13     //ans = (b - a) / x;
14     ans = b / x - a / x;
15     if (a%x == 0)
16         ans++;
17     cout << ans;
18     return 0;
19 }

AtCoder Beginner Contest 048 B - Between a and b

原文：https://www.cnblogs.com/yangyi2120/p/14613655.html