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 $x$

?

Constraints

• $\mathrm{0\le a\le b\le 1018}$

• $\mathrm{1\le x\le 1018}$

 

---

Input

The input is given from Standard Input in the following format:

$a$ $b$ $x$

 Output

Print the number of the integers between $a$

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：

 

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    unsigned long long a, b, x, ans;
    cin >> a >> b >> x;
    if (a > b)
    {
        cout << 0;
        return 0;
    }
    //ans = (b - a) / x;
    ans = b / x - a / x;
    if (a%x == 0)
        ans++;
    cout << ans;
    return 0;
}