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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. const int N = 100005;
  5. const int A = 1000000;
  6.  
  7. int a[N];
  8. int cnt[A + 1];
  9. int n;
  10.  
  11. map<int,int> mp;
  12.  
  13. int sub1()
  14. {
  15.     for(int i = 1; i <= n; i++)
  16.     {
  17.         cnt[a[i]]++;
  18.     }
  19.  
  20.     for(int i = 0; i <= A; i++)
  21.     {
  22.         if(cnt[i] % 2 == 1)
  23.             return i;
  24.     }
  25. }
  26.  
  27. int sub2_solve1()
  28. {
  29.     for(int i = 1; i <= n; i++)
  30.     {
  31.         mp[a[i]]++;
  32.     }
  33.  
  34.     for(pair<int,int> x:mp)
  35.     {
  36.         if(x.second % 2 == 1)
  37.             return x.first;
  38.     }
  39. }
  40.  
  41. int sub2_solve2()
  42. {
  43.     sort(a + 1, a + 1 + n);
  44.  
  45.     int cnt = 1;
  46.     for (int i = 2; i <= n; i++)
  47.     {
  48.         if (a[i] == a[i - 1])
  49.         {
  50.             ++cnt;
  51.         }
  52.  
  53.         else
  54.         {
  55.             if (cnt % 2 == 1) return a[i - 1];
  56.             cnt = 1;
  57.         }
  58.     }
  59.  
  60.     if (cnt % 2 == 1) return a[n];
  61. }
  62.  
  63. int sub2_solve3()
  64. {
  65.     int ans = 0;
  66.  
  67.     for(int i = 1; i <= n; i++)
  68.     {
  69.         ans ^= a[i];
  70.     }
  71.  
  72.     return ans;
  73. }
  74.  
  75. int main() {
  76.     ios_base::sync_with_stdio(false);
  77.     cin.tie(nullptr);
  78.     cout.tie(nullptr);
  79.     freopen("CHIECGIAY.INP", "r", stdin);
  80.     freopen("CHIECGIAY.OUT", "w", stdout);
  81.     cin >> n;
  82.     int MaxA = -1;
  83.     for(int i = 1; i <= n; i++)
  84.     {
  85.         cin >> a[i];
  86.         MaxA = max(MaxA, a[i]);
  87.     }
  88.  
  89.     if (MaxA <= 1e6) cout<<sub1();
  90.     else cout<<sub2_solve3();
  91.  
  92.     return 0;
  93. }
  94.  
Success #stdin #stdout 0.01s 5316KB
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https://ideone.com/awpYV8
language:
C++14 (clang 8.0)
created:
38 days ago
visibility:
secret

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