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20 lines
600 B
C++
20 lines
600 B
C++
#define _CRT_SECURE_NO_WARNINGS
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#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
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#include <bits/stdc++.h>
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using namespace std;
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int main()
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{
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int n;
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cin >> n;
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vector<int> v1(n), v2;
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v2.reserve(n * (n - 1) / 2);
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for (auto &x : v1)
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cin >> x;
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for (int i = 0; i < n; i++)
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for (int j = 0; j < i; j++)
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v2.push_back(v1[i] + v1[j]);
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sort(v2.begin(), v2.end());
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cout << count_if(v1.begin(), v1.end(), bind(binary_search<decltype(v2)::iterator, decltype(v2)::value_type>, v2.begin(), v2.end(), placeholders::_1));
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return 0;
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}
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