lessons/参考实现/03-Bitset/AtCoder-abc258_g.cpp

#include <bitset>
#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; cin >> n;
    constexpr int max_n = 3000;
    vector<bitset<max_n>> neighbor(n);
    vector<string> matrix(n);
    for (int i = 0; i < n; ++i) {
        cin >> matrix[i];
        for (int j = 0; j < n; ++j) if (matrix[i][j] == '1') neighbor[i].set(j);
    }
    long long sum = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) if (matrix[i][j] == '1') {
            sum += static_cast<long long>((neighbor[i] & neighbor[j]).count());
        }
    }
    cout << sum / 3 << '\n';
}