C++ 代码优化和运行错误排查：#pragma GCC optimize 详解

///'#pragma GCC optimize//(1//)//n#pragma GCC optimize//(2//)//n#pragma GCC optimize//(3,///'Ofast///',///'inline///'//)//n#include//<bits///stdc++.h//>/nusing namespace std;/ninline static const nullptr_t _={//n ios_base::sync_with_stdio//(0//);//n cin.tie//(nullptr//),cout.tie//(nullptr//);//n return nullptr;//n}();//nint n,m,x,y;pair//<int,int//> a[305],b[105];bitset//<305//> vis;double ans=INT_MAX,s;//nvector//<pair//<int,double//> //> g[305];//nvoid bfs//(int i,double s=0//){//n queue//<pair//<int,double//> //> q;//n q.push//(make_pair//(i,s//)//);//n vis[i]=1;//n while//(!q.empty//()//){//n pair//<int,double//> x=q.front//();//n if//(x.first==n+1//) ans=min//(ans,x.second//);//n q.pop//();//n for//(int j=0;j//<g[x.first].size//();j++//){//n if//(!vis[g[x.first][j].first]//){//n vis[g[x.first][j].first]=1;//n q.push//(make_pair//(g[x.first][j].first,x.second+g[x.first][j].second//)//);//n }//n }//n }//n}//nbool check//(int i,int j//){//n double k=//(a[j].second-a[i].second//)/////(a[j].first-a[i].first//),b0=a[i].second-a[i].firstk;//n for//(int i=1;i<=m;i++//) if//(fabs//(b[i].firstk+b0-b[i].second//)<=1e-6//) return 0;//n return 1;//n}//ntemplate//<typename T1//>//ndouble dis//(pair//<T1,T1//> p1,pair//<T1,T1//> p2//){//n/treturn sqrt//((p1.first-p2.first//)(p1.first-p2.first//)+(p1.second-p2.second//)(p1.second-p2.second//)//);//n}//nint main//() {//n cin>>x>>y>>n>>m;//n for//(int i=1;i<=n;i++//) cin>>a[i].first>>a[i].second;//n for//(int i=1;i<=m;i++//) cin>>b[i].first>>b[i].second;//n for//(int i=1;i<=n;i++//) for//(int j=1;j<=n;j++//) if//(check//(i,j//)//) g[i].emplace_back//(j,dis//(a[i],a[j]//)//);//n for//(int i=1;i<=n;i++//) g[i].emplace_back//(n+1,dis//(a[i],make_pair//(x,y//)//)*2//);//n vis[1]=1;//n bfs//(1//);//n cout//((int//)round//(ans//)//)<<'//n';//n return 0;//n}/