L1 读入

目录

• 代码实现和计时
  • 0. 数据生成器
  • 1. 普通快读
  • 2. scanf()
  • 3. 普通cin>>
  • 4. cin>> + ios::sync_with_stdio(false)
• 结论

此篇blog比较了OI里常用四种读入方式

代码实现和计时

0. 数据生成器

(code):

#include<cstdio>
#include<cstdlib>
#include<windows.h>
#define Re register
using namespace std;
const int N=1919810;
int main(){
    freopen("sample.txt","w",stdout);
    srand(GetTickCount());
    for(Re int i=1;i<=N;++i)
        printf("%d ",rand()-16374);
}

1. 普通快读

(code):

//1919810个数据约210ms
#include<cstdio>
#include<windows.h>
#define Re register
using namespace std;
inline int read(){
    Re int x=0,f=1;
    Re char c;
    while((c=getchar()) && (c<'0' || c>'9'))
        if(c=='-')
            f=(int)0xFFFFFFFF;
    do
        x=(x<<3)+(x<<1)+(c^48);
    while((c=getchar()) && c>='0' && c<='9');
    return x*f;
}
const int N=1919810;
long Tick1,Tick2;
int main(){
    freopen("sample.txt","r",stdin);
    Tick1=GetTickCount();
    for(int i=1;i<=N;++i)
        read();
    Tick2=GetTickCount();
    printf("%ld",Tick2-Tick1);
}

2. scanf()

(code):

//1919810个数据约670ms
#include<cstdio>
#include<windows.h>
using namespace std;
const int N=1919810;
int n;
long Tick1,Tick2;
int main(){
    freopen("sample.txt","r",stdin);
    Tick1=GetTickCount();
    for(int i=1;i<=N;++i)
        scanf("%d",&n);
    Tick2=GetTickCount();
    printf("%ld",Tick2-Tick1);
}

3. 普通cin>>

(code):

//1919810个数据约1.3s
#include<iostream>
#include<cstdio>
#include<windows.h>
using namespace std;
const int N=1919810;
int n;
long Tick1,Tick2;
int main(){
    freopen("sample.txt","r",stdin);
    Tick1=GetTickCount();
    for(int i=1;i<=N;++i)
        cin>>n;
    Tick2=GetTickCount();
    cout<<Tick2-Tick1;
}

4. cin>> + ios::sync_with_stdio(false)

(code):

//1919810个数据约250ms
#include<iostream>
#include<cstdio>
#include<windows.h>
using namespace std;
const int N=1919810;
int n;
long Tick1,Tick2;
int main(){
    freopen("sample.txt","r",stdin);
    ios::sync_with_stdio(false);
    Tick1=GetTickCount();
    for(int i=1;i<=N;++i)
        cin>>n;
    Tick2=GetTickCount();
    cout<<Tick2-Tick1;
}

结论

• 普通快读略快于优化cin>>
• 如果懒得写快读就写优化cin>>即可