优化时间的实用小技巧

1.火车头

#pragma GCC optimize(1)

#pragma GCC optimize(2)

#pragma GCC optimize(3)

#pragma GCC optimize(O2)

#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")

2.函数前加inline

3.int，long long前加register

4.i++变成++i

5.位运算

6.快读快输(不建议用快输,容易莫名其妙的WA

inline int read(){

re int x(0),y(1);

re char ch=getchar();

while(ch<'0'||ch>'9'){

if(ch=='-') y=-1;

ch=getchar();

}

while(ch>='0'&&ch<='9'){

x=(x<<3)+(x<<1)+ch-'0';

ch=getchar();

}

return x*y;

}

inline void write(re int x){

re char F[201];

re int tmp(x>0?x:-x);

if(x<0) putchar('-');

re int cnt(0);

while(tmp>0){

F[++cnt]=tmp%10+'0';

tmp/=10;

}

while(cnt>0){

putchar(F[--cnt]);

}

}

用法：n=read(),write(ans)

以上都是大多数人知道的，那么接下来让我给大家分享点不太常见的卡常技巧吧：

7.i=1改成i(1)

8.开一个数组a[N],N要为奇数（别问我为什么，问就是玄学

9.i-- 改成 --i,i++和++i 改成 i=-~i

10.cout<<endl 改成 cout<<"\n";

11.嫌上面6麻烦可以用cin，cout并加上

std::ios::sync_with_stdio(false)

cin.tie(0);

cout.tie(0);

12.嫌11麻烦也可以用scanf，千万不要用裸的cin，cout！！！

13.不要在循环内定义变量（被卡过就知道有多痛苦

14.return 0;改成exit(0);

说实话，其实就火车头和快读有点儿用，其他的优化不大

好的，那么以上就是这篇题解的内容了，希望能帮助到大家

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