C和C ++中执行时间的差异 [英] Difference in execution time in C and C++

问题描述

我最近发现这个网站叫codechef，你可以提交问题的解决方案。
我为一个问题提交了两个答案，一个在C中，另一个在C ++中。两个代码几乎相同。但是当我在C提交的代码在4.89s执行时，我在C ++提交的代码超时（超过8秒）。这怎么可能？

问题是：

p>

输入以两个正整数nk（n，k <= 107）开始。接下来的n行输入包含一个正整数ti，每个不大于10 ^ 9。

输出

写一个整数到输出，表示多少整数ti可以被k整除。

 示例
 
输入：
 7 3 
 1 
 51 
 966369 
 7 
 9 
 999996 
 11 
 
输出：
 4 
  

C：

 ＃include< stdio.h> 
 
 int main（）{
 
 int n，k，t; 
 scanf（％d％d，& n，& k）; 
 int i，num = 0; 
 for（i = 0; i  scanf（％d，& t）; 
 if（t％k == 0）num ++; 
} 
 
 printf（％d，num）; 
 
 return 0; 
} 
  

我在C ++中的代码：

 ＃include< iostream> 
 
 using namespace std; 
 
 int main（）{
 
 int n，k，t，num = 0; 
 cin>>> n>> k; 
 for（int i = 0; i  cin>> t; 
 if（t％k == 0）num ++; 
} 
 
 cout<< num; 
 return 0; 
} 
  

解决方案

b

默认情况下，cin / cout会浪费时间与C库的stdio缓冲区同步，以便您可以自由地混合使用cin / cout操作对scanf / printf的调用。您可以使用 std :: ios_base :: sync_with_stdio（false）;

关闭此功能。采取将或多或少相似我期望

I recently found this site called codechef, where you can submit solutions to problems. I had submitted two answers for a question, one in C and the other in C++. Both codes are almost the same. But when the code I submitted in C was executed in 4.89s, the code I submitted in C++ was timed out (more than 8 seconds). How is this possible? Where does the time go?

The question was:

Input

The input begins with two positive integers n k (n, k<=107). The next n lines of input contain one positive integer ti, not greater than 10^9, each.

Output

Write a single integer to output, denoting how many integers ti are divisible by k.

Example

Input:
7 3
1
51
966369
7
9
999996
11

Output:
4

My code in C:

 #include<stdio.h>

 int main()  {

   int n,k,t;
   scanf("%d %d",&n,&k);
   int i,num=0;
   for(i=0;i<n;i++)  {
     scanf("%d",&t);
     if(t%k==0)  num++;
   }     

   printf("%d",num);

   return 0;
 }

My Code in C++:

 #include<iostream>

 using namespace std;

 int main()  {

   int n, k, t,num=0;
   cin>>n>>k;
   for(int i=0;i<n;i++)  {
     cin>>t;
     if(t%k==0)  num++;
   }

   cout<<num;
   return 0;
 } 

解决方案

The code is not really the same even though they do the same thing

The c++ version uses cin and streams which are slower than scanf etc by default.

By default, cin/cout waste time synchronizing themselves with the C library’s stdio buffers, so that you can freely intermix calls to scanf/printf with operations on cin/cout. You can turn this off with std::ios_base::sync_with_stdio(false);

By doing this the time taken will more or less be similar I would expect

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