读入优化

int read( ){
    int ans=0,op=1;
    char c;
    c=getchar();
    for(;(c<'0'||c>'9')&&c!='-';c=getchar());
    if(c=='-') op=-1,c=getchar( );
    for(;(c>='0'&&c<='9');c=getchar( )) ans*=10,ans+=c-'0';
    return ans*op;
} 
c^48==c-'0' 
n=read();

使用getchar()

来源：https://www.cnblogs.com/liuziwen0224/p/11992368.html