GCC 内置位运算

int __builtin_clz(unsigned int x);      //求前缀0的个数
int __builtin_ctz(unsigned int x);      //求后缀0的个数
int __builtin_ffs(unsigned int x);      //x的二进制末尾最后一个1的位置，从1开始
int __builtin_popcount(unsigned int x); //x二进制中1的个数，相当于bitset::count()
int __builtin_parity(unsigned int x);   //判断x的二进制中1的个数的奇（1）偶（0）性，这些函数都有相应的usigned long和usigned long long版本，只需要在函数名后面加上l或ll就可以了，比如__builtin_clzll

开栈

For C++

#pragma comment(linker, "/STACK:102400000,102400000") //For C++

For G++

int main() //For G++
{
	int size = 256 << 20; //256MB
	char *p = (char *)malloc(size) + size;
	__asm__ __volatile__("movq %0, %%rsp\n" ::"r"(p)); //64bit，一定要最后写一句`exit(0);`退出程序，否则会得到非零退出的错误，可能RE。
}

读入优化

C 文件指针版

ll getll(FILE *in = stdin)
{
	ll val = 0, sgn = 1, ch = getc(in);
	for (; !isdigit(ch) && ch != EOF; ch = getc(in))
		if (ch == '-')
			sgn = -sgn;
	for (; isdigit(ch); ch = getc(in))
		val = val * 10 + ch - '0';
	return ungetc(ch, in), sgn * val;
}
lf getlf(FILE *in = stdin)
{
	lf val = getll(in), p = val < 0 ? -1 : 1;
	ll ch = getc(in);
	if (ch == '.')
		for (ch = getc(in); isdigit(ch); ch = getc(in))
			val += (p /= 10) * (ch - '0');
	return ungetc(ch, in), val;
}

仿 C++IO 流沙雕版

使用前

使用后

#define cin kin
struct Istream
{
	char b[20 << 20], *i, *e; //20MB
	Istream(FILE *in) : i(b), e(b + fread(b, sizeof(*b), sizeof(b), in)) {}
	bool eof() const
	{
		return i == e;
	}
	Istream &operator>>(long long &val)
	{
		return val = strtoll(i, &i, 10 /*进制，取值2~36*/), *this;
	}
	Istream &operator>>(ll &val) //极限快
	{
		while (*i < '0')
			++i; //无符号
		for (val = 0; *i >= '0'; ++i)
			val = (val << 3) + (val << 1) + *i - '0';
		return *this;
	}
	Istream &operator>>(double &val)
	{
		return val = strtod(i, &i), *this;
	}
	Istream &operator>>(string &s)
	{
		while (!eof() && isspace(*i))
			++i;
		for (s.clear(); !eof() && !isspace(*i); ++i)
			s += *i;
		return *this;
	}
} kin(stdin);