mirror of
https://git.sb/baoshuo/OI-codes.git
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65 lines
1.1 KiB
C++
65 lines
1.1 KiB
C++
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#include <iostream>
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#include <algorithm>
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#include <array>
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#include <vector>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 5005;
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int n, max_dep;
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long long ans;
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std::vector<int> g[N];
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std::array<int, N> f1, f2, cnt;
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void dfs(int u, int f, int d) {
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cnt[d]++;
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max_dep = std::max(max_dep, d);
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for (int v : g[u]) {
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if (v == f) continue;
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dfs(v, u, d + 1);
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}
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n;
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for (int i = 1, u, v; i < n; i++) {
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cin >> u >> v;
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g[u].emplace_back(v);
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g[v].emplace_back(u);
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}
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dfs(1, 0, 1);
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for (int i = 1; i <= n; i++) {
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std::fill(f1.begin(), f1.end(), 0);
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std::fill(f2.begin(), f2.end(), 0);
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for (int u : g[i]) {
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max_dep = 0;
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std::fill(cnt.begin(), cnt.end(), 0);
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dfs(u, i, 1);
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for (int j = 1; j <= max_dep; j++) {
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ans += f1[j] * cnt[j];
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f1[j] += f2[j] * cnt[j];
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f2[j] += cnt[j];
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}
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}
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}
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cout << ans << endl;
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return 0;
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}
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