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  1. #include <cstdio>
  2. #include <bits/stdc++.h>
  3.  
  4. using namespace std;
  5.  
  6. const int N = 1e6 + 3;
  7.  
  8. unordered_map <int, int> M[N];
  9. int n, a[N], mx = 0;
  10.  
  11. int main (){
  12. 	ios_base::sync_with_stdio(0);
  13. 	cin.tie(0);
  14. 	cout.tie(0);
  15. 	cin >> n;
  16. 	for (int i = 0; i < n; ++i){
  17. 		cin >> a[i];
  18. 		M[i].reserve(i);
  19. 		M[i].max_load_factor(0.25);
  20. 	}
  21. 	for (int i = 1; i < n; ++i){
  22. 		for (int j = 0; j < i; ++j){
  23. 			int x = a[i] - a[j];
  24. 			if (M[j].find(-x) != M[j].end()) {
  25. 				int w = M[j].count(-x) + 1;
  26. 				M[i][x] = w;
  27. 				mx = max(mx, w);
  28. 			}
  29. 			else{
  30. 				M[i][x] = 1;
  31. 				mx = max(mx, 1);
  32. 			}
  33. 		}
  34. 	}
  35. 	cout << mx + 1;
  36. 	return 0;
  37. }
Success #stdin #stdout 0.02s 58228KB
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https://ideone.com/wNU6ag
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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