快读

一般的，当要读入的东西常数过大时，就会使用快读，且时间复杂度比\(cin\)低。

代码：

void read(int &x)
{
	x = 0;
	int f = 1;
	char c = getchar();
	while (!('0' <= c && c <= '9'))
	{
		if (c == '-')
		{
			f = -1;
		}
		c = getchar();
	}
	while ('0' <= c && c <= '9')
	{
		x = (x << 1) + (x << 3) + (c ^ 48);
		c = getchar();
	}
	x *= f;
}

使用：

int n;
read(n);

快读的改进

#define getchar()(p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
char buf[1<<21];
char *p1=buf;
char *p2=buf;
void read(int &x)
{
	x = 0;
	int f = 1;
	char c = getchar();
	while (!('0' <= c && c <= '9'))
	{
		if (c == '-')
		{
			f = -1;
		}
		c = getchar();
	}
	while ('0' <= c && c <= '9')
	{
		x = (x << 1) + (x << 3) + (c ^ 48);
		c = getchar();
	}
	x *= f;
}

当然，读字符串还是用\(getchar\)吧……