Help to figure out the error

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During solving this problem, when i submitted the following code with c++ setprecision function i got Wrong answer on test 5.

Code

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin>>n;
    vector<pair<long long,long long>>v;
    long long ans=0;
    for(int i=0; i<n; i++)
    {
        long long x,y;
        cin>>x>>y;
        ans=max(ans,x*y);
        if(x>y)
            swap(x,y);
        v.push_back(make_pair(x,y));
    }
    sort(v.rbegin(),v.rend());
    long long mx=0;
    for(int i=0; i<n; i++)
    {
        ans=max(ans,2LL*v[i].first*min(v[i].second,mx));
        mx=max(mx,v[i].second);
    }
    double res=(ans*1.0)/2.0;
    cout<<fixed<<setprecision(1);
    cout<<res<<'\n';
}

And later the following one got accepted without setprecision.

Code

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin>>n;
    vector<pair<long long,long long>>v;
    long long ans=0;
    for(int i=0; i<n; i++)
    {
        long long x,y;
        cin>>x>>y;
        ans=max(ans,x*y);
        if(x>y)
            swap(x,y);
        v.push_back(make_pair(x,y));
    }
    sort(v.rbegin(),v.rend());
    long long mx=0;
    for(int i=0; i<n; i++)
    {
        ans=max(ans,2LL*v[i].first*min(v[i].second,mx));
        mx=max(mx,v[i].second);
    }
    /*
    double res=(ans*1.0)/2.0;
    cout<<fixed<<setprecision(1);
    cout<<res<<'\n';
    */
    cout<<ans/2;
    if(ans&1)
        cout<<".5\n";
    else
        cout<<".0\n";
}

My question is, what i did wrong in the first one?

Thank You...

Upd: Got the error. Should use `long double` instead `double`

Comments (3)

Write comment?

darya_navard

18 months ago, # |

← Rev. 2 →

-6

→ Reply

fmoeran

I can't see the actual wrong answer message so this is just guesses. It could be that when you're dividing by 2 in the first solution, ans is so large that floating point precision is too much of a problem (i.e. rounds it closer to .4 or .6 instead of .5)

rkb_rd

18 months ago, # ^ |

got it. you are right. thanks

rkb_rd's blog

Upd: Got the error. Should use long double instead double

Upd: Got the error. Should use `long double` instead `double`