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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. long long sumlm(long long l, long long m){
  5.     return m*(m+1)/2 - (l-1)*l/2;
  6. }
  7.  
  8. long long summ1r(long long m, long long r){
  9.     return r*(r+1)/2 - m*(m+1)/2;
  10. }
  11.  
  12. int main() {
  13.     long long l, r;
  14.     cin >> l >> r;
  15.     long long tl = l, tr = r;
  16.     long long mid;
  17.  
  18.     while(tl <= tr){
  19.         mid = (tl + tr) / 2;
  20.         long long lm = sumlm(l, mid);
  21.         long long mr = summ1r(mid, r);
  22.         if (lm <= mr) tl = mid + 1;
  23.         else tr = mid - 1;
  24.     }
  25.  
  26.     long long best = mid;
  27.     long long diff = LLONG_MAX;
  28.     for(long long x = mid-1; x <= mid+1; x++){
  29.         if(x < l || x > r) continue; 
  30.         long long cur_diff = abs(sumlm(l, x) - summ1r(x, r));
  31.         if(cur_diff < diff){
  32.             diff = cur_diff;
  33.             best = x;
  34.         }
  35.     }
  36.  
  37.     cout << best;
  38. }
Success #stdin #stdout 0.01s 5324KB
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https://ideone.com/OWciQt
language:
C++14 (gcc 8.3)
created:
16 days ago
visibility:
public

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