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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. using ll = long long;
  4. bool csc(ll x, const unordered_set<ll> &st) {
  5.     for (auto y : st) {
  6.         ll sum = x + y;
  7.         if (sum % 2 == 0) {
  8.             long long mid = sum / 2;
  9.             if (st.count(mid)) return true;
  10.         }
  11.     }
  12.     return false;
  13. }
  14. int maxlen(const vector<long long> &a) {
  15.     unordered_set<ll> st;
  16.     int l = 0, ans = 0;
  17.     for (int r = 0; r < (int)a.size(); r++) {
  18.         while (st.count(a[r])) {
  19.             st.erase(a[l]);
  20.             l++;
  21.         }
  22.         while (csc(a[r], st)) {
  23.             st.erase(a[l]);
  24.             l++;
  25.         }
  26.         st.insert(a[r]);
  27.         ans = max(ans, r - l + 1);
  28.     }
  29.     return ans;
  30. }
  31. int main(){
  32.     ll n;
  33.     cin >> n;
  34.     vector<ll> a(n+1);
  35.     for( int i = 1 ; i<= n ; i++ ) cin >> a[i];
  36.     cout << maxlen(a);
  37.     return 0;
  38. }
  39.  
  40.  
Success #stdin #stdout 0s 5324KB
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https://ideone.com/SeOreI
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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