读入输出优化

读入输出优化

这里介绍了快读快写、O2 优化、关闭同步流。

时间比较：快读快些 \(\le\) \(c\) 语言输入输出 \(\le\) 关闭同步流 \(\le\) \(c++\) 语言输入输出。

大家可以根据注释理解一下代码。

// 快读 
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  for (; ch < '0' || ch > '9'; (ch == '-') && (f = -1), ch = getchar) {  // 如果 ch 为负号，就设定 f=-1 
	}
  for (; ch >= '0' && ch <= '9'; x = x * 10 + ch - '0', ch = getchar) {  // 计算 x 并读入 
	}
  return x * f;                                                          // 输出 x*f 
}

// 优化快读
char *p1, *p2, buf[100000];

#define nc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2) ? EOF : *p1++)

inline int read() {  // 代码意思同上 
  int x = 0, f = 1;
  char ch = nc();
  for (; ch < '0' || ch > '9'; (ch == '-') && (f = -1), ch = nc()) {
	}
  for (; ch >= '0' && ch <= '9'; x = x * 10 + ch - '0', ch = nc()) {
	}
  return x * f;
}

// 快写
void write(int x) {
  (x < 0) && (putchar('-'), x = -x);  // 如果 x 为负数，就先输出符号，再输出它的相反数 
  (x > 9) && (write(x / 10), 0);      // 如果 x 不为一位数就先输出前面的（递归），再输出个位 
  putchar(x % 10 + '0');              // 输出个位 
}

// O2 优化
#pragma GCC optimize(2)

// 关闭同步流
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0); 

其他

// 火车头
#pragma GCC optimize(3)
#pragma GCC target("avx")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-fwhole-program")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-fstrict-overflow")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-skip-blocks")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("-funsafe-loop-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#pragma GCC optimize(2)