SuperJava's blog

By SuperJava, history, 3 months ago, In English,

I used 600B - Queries about less or equal elements to test those and used the same code but with change in input and output streams.

  Cin And Cout   Scanf And Printf
 GNU C++ 5.1.0  358ms Submission:35214275  155ms Submission:35214230
 GNU C++11 5.1.0  343ms Submission:35214311  156ms Submission:35214295
 GNU C++14 6.4.0  187ms Submission:35214315  186ms Submission:35214352
 GNU C++17 7.2.0  187ms Submission:35214359  187ms Submission:35214322

Looks like that scanf&printf is almost the same but cin&cout is slower under c++14.

Don't use cin&cout under c++14 to avoid TLE. Otherwise it is as good as scanf&printf and maybe better!

Scanf And Printf Code

#include <bits/stdc++.h>
using namespace std;
int n,m,val;
vector<int> a;
int main() {
	scanf("%d%d",&n,&m);
	for(int i = 0;i < n;i++){
		scanf("%d",&val);
		a.push_back(val);
	}
	sort(a.begin(),a.end());
	for(int i = 0;i < m;i++){
		int b;
		scanf("%d",&b);
		printf("%d ",upper_bound(a.begin(),a.end(),b)-a.begin());
	}
	return 0;
}

Cin And Cout Code

#include <bits/stdc++.h>
using namespace std;
int n,m,val;
vector<int> a;
int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cin >> n >> m;
	for(int i = 0;i < n;i++){
		cin >> val;
		a.push_back(val);
	}
	sort(a.begin(),a.end());
	for(int i = 0;i < m;i++){
		int b;
		cin >> b;
		cout << upper_bound(a.begin(),a.end(),b)-a.begin() << " ";
	}
	return 0;
}
 
 
 
 
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3 months ago, # |
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Auto comment: topic has been updated by SuperJava (previous revision, new revision, compare).

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3 months ago, # |
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How can you prove this isn't a result of changes to vector class, or upper bound method.

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    3 months ago, # ^ |
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    It's the same code and the same input so the vector and the upper bound should do the same. Cin&Cout was obviously doing bad under c++14. It's about the double. That's my point in this blog.

    Thank you for the point!

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      3 months ago, # ^ |
      Rev. 5   Vote: I like it 0 Vote: I do not like it

      yeah that's exactly my point. You don't know if the vector makes it slower or the cin/cout.

      I saw an earlier benchmark from a solely-input program, if I remember cin/cout is twice as fast as scanf/printf, but I can't find it anymore unfortunately.

      EDIT: found it http://codeforces.com/blog/entry/5217

      cin/cout significantly better. note the blog is more than 5 years ago, so c++14 didn't exist

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        3 months ago, # ^ |
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        That's a nice blog but I tested more than one time and I do not know how vector class can change the result while the same code on scanf version doesn't.

        Looks like it is depends in c++ version and the type of the input as the blog mentioned.

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          3 months ago, # ^ |
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          I am sorry. I wasn't thinking at all earlier. You are right.

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3 months ago, # |
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I think it would also be interesting if you tested the code without ios_base::sync_with_stdio(false); for comparison purposes :)