mirror of
https://git.sb/baoshuo/OI-codes.git
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144 lines
2.9 KiB
C++
144 lines
2.9 KiB
C++
#include <iostream>
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#include <algorithm>
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#include <iterator>
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#include <queue>
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#include <set>
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#include <unordered_map>
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#include <utility>
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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 = 55,
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M = (N << 1) * (N << 1);
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const int INF = 0x3f3f3f3f;
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int n, cnt, s, t, cost;
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int idx, head[N << 1], ver[M << 1], next[M << 1];
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std::pair<int, int> edge[M << 1];
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std::unordered_map<int, int> cnt_x, cnt_y, id_x, id_y;
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std::set<std::pair<int, int>> set;
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int dist[N << 1];
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bool vis[N << 1];
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void add(int u, int v, int flow, int cost) {
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next[idx] = head[u];
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ver[idx] = v;
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edge[idx] = std::make_pair(flow, cost);
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head[u] = idx++;
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}
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bool spfa() {
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std::fill(std::begin(vis), std::end(vis), false);
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std::fill(std::begin(dist), std::end(dist), INF);
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std::queue<int> q;
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q.emplace(s);
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dist[s] = 0;
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vis[s] = true;
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while (!q.empty()) {
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int u = q.front();
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q.pop();
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vis[u] = false;
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for (int i = head[u]; ~i; i = next[i]) {
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int v = ver[i],
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flow = edge[i].first,
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cost = edge[i].second;
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if (flow && dist[v] > dist[u] + cost) {
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dist[v] = dist[u] + cost;
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if (!vis[v]) {
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q.emplace(v);
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vis[v] = true;
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}
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}
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}
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}
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return dist[t] != INF;
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}
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int dinic(int u, int limit) {
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if (u == t) return limit;
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int flow = 0;
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vis[u] = true;
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for (int i = head[u]; ~i && flow < limit; i = next[i]) {
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int v = ver[i],
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f = edge[i].first,
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w = edge[i].second;
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if (dist[v] == dist[u] + w && f && !vis[v]) {
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int k = dinic(v, std::min(f, limit - flow));
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if (!k) dist[v] = INF;
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edge[i].first -= k;
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edge[i ^ 1].first += k;
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flow += k;
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cost += k * w;
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}
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}
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vis[u] = false;
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return flow;
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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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std::fill(std::begin(head), std::end(head), -1);
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cin >> n;
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for (int i = 1, x, y; i <= n; i++) {
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cin >> x >> y;
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cnt_x[x]++, cnt_y[y]++;
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set.emplace(x, y);
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if (!id_x.count(x)) id_x[x] = ++cnt;
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if (!id_y.count(y)) id_y[y] = ++cnt;
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}
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s = 0, t = cnt + 1;
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for (auto o : id_x) {
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add(s, o.second, cnt_x[o.first], 0);
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add(o.second, s, 0, 0);
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}
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for (auto o : id_y) {
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add(o.second, t, cnt_y[o.first], 0);
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add(t, o.second, 0, 0);
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}
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for (auto a : id_x) {
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for (auto b : id_y) {
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if (set.count(std::make_pair(a.first, b.first))) {
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add(a.second, b.second, 1, 1);
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add(b.second, a.second, 0, -1);
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} else {
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add(a.second, b.second, 1, 0);
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add(b.second, a.second, 0, 0);
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}
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}
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}
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while (spfa()) dinic(s, INF);
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cout << cost << endl;
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return 0;
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}
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