Submission #70413488

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Source Code Expand

#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = std::forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = std::forward<U>(y), true); }

template <class T> void mkuni(std::vector<T>& v) {
    std::ranges::sort(v);
    auto result = std::ranges::unique(v);
    v.erase(result.begin(), result.end());
}

template <class T> int lwb(const std::vector<T>& v, const T& x) {
    return std::distance(v.begin(), std::ranges::lower_bound(v, x));
}

using namespace std;

using ll = long long;

void solve() {
    int N;
    cin >> N;
    vector<int> A(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }

    map<int, int> mp;
    for (int i = 0; i < N; i++) {
        mp[A[i]]++;
    }

    ll ans = 0;
    for (auto [_, cnt] : mp) {
        ans += 1LL * cnt * (cnt - 1) / 2 * (N - cnt);
    }

    cout << ans << "\n";
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    solve();
    return 0;
}

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