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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int long long
  4. signed main()// no idea if this correct or not 
  5. {
  6.     int n,k;
  7.     cin>>n>>k;
  8.     int l=1,r=1e10,mid;
  9.     while(l<=r)
  10.     {
  11.         mid=l+(r-l)/2;
  12.         int y=((mid*(mid+1))/2-k);
  13.         if(y>=0)
  14.         {
  15.             if(mid+y==n)
  16.             {
  17.                 cout<<y;
  18.                 return 0;
  19.             }
  20.             else if(mid+y>n)
  21.             {
  22.                 r=mid-1;
  23.             }
  24.             else
  25.                 l=mid+1;
  26.         }
  27.         else
  28.             l=mid+1;
  29.     }
  30.     // for(int i=1;i<=20;i++)//test the brute force idea 
  31.     // {
  32.     //     int y=(i*(i+1))/2-k;
  33.     //     if(i+y==n)
  34.     //         cout<<y;
  35.     // }
  36. }
  37.  
  38. /*
  39.  
  40. 5 0
  41.  
  42. +1 +2 -1 -1 -1
  43.  
  44. */
Success #stdin #stdout 0.01s 5296KB
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https://ideone.com/34evkx
language:
C++14 (gcc 8.3)
created:
5 days ago
visibility:
public

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