rishi_07's blog

Please explain the difference between the two solutions ACM ICPC 2018 online round
By rishi_07, history, 9 years ago, In English

These are my codes for the problem Compression Algorithm of ACM ICPC 2018 online round.
I don't understand what is the problem with the first solution.
Note: The expected precision was 10^-6.
Image 1
Image 2

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9 years ago, hide # |
 
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Auto comment: topic has been updated by rishi_07 (previous revision, new revision, compare).

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9 years ago, hide # |
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Well they say "Your answer will be considered correct if the absolute error is less than 10 - 6". With printf("%.6lf") there is possibility you will print something with error equal to 10 - 6 which is considered wrong.

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    9 years ago, hide # ^ |
     
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    Hi, please check the first image. There I used setprecision(10). Still WA. This is not only my case, check this discussion on codechef Link

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9 years ago, hide # |
 
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I can explain why the setprecision code gives WA but I have no idea about the printf . setprecision includes the number of digits before the decimal point also . So setting it to 9 + 6 should work.

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    9 years ago, hide # ^ |
     
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    In this Link user swetankmodi claimed to have used setprecision(18) but still got WA.

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      9 years ago, hide # ^ |
       
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      #include <bits/stdc++.h>
using namespace std;
 
int main(void)
{
	ios::sync_with_stdio(false); cin.tie(0);
	int t; cin >> t;
	while(t--)
	{
		long long int n, k; cin >> n >> k;
		long double ans = 2.0 * ((k-1)*n + 1) / k;
		cout << fixed << setprecision(16) << ans << endl;
	}
}

      This gave us AC

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      9 years ago, hide # ^ |
       
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      yes, but the solution posted by @bhishma uses long double but I used only double. Maybe that caused the issue?

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    9 years ago, hide # ^ |
     
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    You're wrong. From http://www.cplusplus.com/reference/iomanip/setprecision/
    "Sets the decimal precision to be used to format floating-point values on output operations". Beside we submitted with setprecision(8) and it got accepted.

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      9 years ago, hide # ^ |
       
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      Actually my main language is Java so I might be wrong , but I have seen this issue in some old codeforces blog . In that case how can you explain this

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9 years ago, hide # |
 
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There is a difference between cout<<fixed<<setprecision(10)<<x; and cout<<setprecision(10)<<x;

Example:

long double x=1000000000000.13232; cout<<fixed<<setprecision(10)<<x;

Output: 1000000000000.1323242188

long double x=1000000000000.13232; cout<<setprecision(10)<<x;

Output: 1e+12

If u dont use fixed and the number is reasonably large u might lose precision

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