【CodeForces】CF1A Theatre Square

https://www.luogu.com.cn/problem/CF1A

题面翻译：
用 a × a a times a a×a的石板覆盖 n × m n times m n×m的长方形广场，允许石板覆盖的区域超出广场，不允许打破石板，石板的两侧应平行于广场两侧，要求覆盖完广场所需的石板数量最少是多少。

题目描述：
Theatre Square in the capital city of Berland has a rectangular shape with the size n × m n×m n×m meters. On the occasion of the city’s anniversary, a decision was taken to pave the Square with square granite flagstones. Each flagstone is of the size a × a a×a a×a .

What is the least number of flagstones needed to pave the Square? It’s allowed to cover the surface larger than the Theatre Square, but the Square has to be covered. It’s not allowed to break the flagstones. The sides of flagstones should be parallel to the sides of the Square.

输入格式：
The input contains three positive integer numbers in the first line: n , m n,m n,m and a a a ( 1 ≤ n , m , a ≤ 1 0 9 1leq n,m,aleq10^{9} 1≤n,m,a≤109).

输出格式：
Write the needed number of flagstones.

答案即为 ⌈ n / a ⌉ × ⌈ m / a ⌉ lceil n/arceil times lceil m/arceil ⌈n/a⌉×⌈m/a⌉。C++里的向上取整可以写成(n + a - 1) / a。代码如下：

#include 
using namespace std;

int main(){
  long long n, m, a;
  cin >> n >> m >> a;
  n = (n + a - 1) / a;
  m = (m + a - 1) / a;
  cout << n * m << endl;
}

时空复杂度 O ( 1 ) O(1) O(1)。