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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. inline long long isqrt(long long n){
  5.     long double N = n;
  6.     N = sqrtl(N);
  7.     long long sq = N - 2;
  8.     sq = max(sq, 0LL);
  9.     while(sq * sq < n){
  10.         sq++;
  11.     }
  12.     if((sq * sq) == n) return sq;
  13.     return sq - 1;
  14. }
  15.  
  16. set<long long> a;
  17. int maxSize = 10000;
  18.  
  19. int main(){
  20.     for (int i = 1; i <= 20; i++) {
  21.         a.insert(i);
  22.     }
  23.     while (a.size() <= maxSize) {
  24.         set<long long> s = a;
  25.         for (auto x : a) {
  26.             for (auto y : a) {
  27.                 s.insert(x * x + y * y);
  28.             }
  29.         }
  30.         for (auto x : a) {
  31.             for (auto y : a) {
  32.                 for (auto z : a) {
  33.                     int d2 = x * x + y * y - z * z;
  34.                     int d = isqrt(d2);
  35.                     if (d2 == d * d && d > 0) {
  36.                         s.insert(d);
  37.                     }
  38.                 }
  39.             }
  40.         }
  41.         a = s;
  42.     }
  43.     int i = 1;
  44.     for (auto x : a) {
  45.         if (x != i) {
  46.             cout << "The first integer that is not in S is " << x << endl;
  47.             break;
  48.         }
  49.         ++i;
  50.     }
  51.     return 0;
  52. }
Success #stdin #stdout 1.16s 5324KB
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Standard input is empty
stdout
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The first integer that is not in S is 640
https://ideone.com/dEJ4EI
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
public

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