#1784. 【2017.3长乐省选集训Day4T2】猜测

https://sjzezoj.com/submission/65322

S2OJ/1784/1784.cpp

@@ -0,0 +1,143 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <queue>
+#include <set>
+#include <unordered_map>
+#include <utility>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 55,
+          M = (N << 1) * (N << 1);
+const int INF = 0x3f3f3f3f;
+
+int n, cnt, s, t, cost;
+int idx, head[N << 1], ver[M << 1], next[M << 1];
+std::pair<int, int> edge[M << 1];
+std::unordered_map<int, int> cnt_x, cnt_y, id_x, id_y;
+std::set<std::pair<int, int>> set;
+int dist[N << 1];
+bool vis[N << 1];
+
+void add(int u, int v, int flow, int cost) {
+    next[idx] = head[u];
+    ver[idx] = v;
+    edge[idx] = std::make_pair(flow, cost);
+    head[u] = idx++;
+}
+
+bool spfa() {
+    std::fill(std::begin(vis), std::end(vis), false);
+    std::fill(std::begin(dist), std::end(dist), INF);
+
+    std::queue<int> q;
+
+    q.emplace(s);
+    dist[s] = 0;
+    vis[s] = true;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        vis[u] = false;
+
+        for (int i = head[u]; ~i; i = next[i]) {
+            int v = ver[i],
+                flow = edge[i].first,
+                cost = edge[i].second;
+
+            if (flow && dist[v] > dist[u] + cost) {
+                dist[v] = dist[u] + cost;
+
+                if (!vis[v]) {
+                    q.emplace(v);
+                    vis[v] = true;
+                }
+            }
+        }
+    }
+
+    return dist[t] != INF;
+}
+
+int dinic(int u, int limit) {
+    if (u == t) return limit;
+
+    int flow = 0;
+
+    vis[u] = true;
+
+    for (int i = head[u]; ~i && flow < limit; i = next[i]) {
+        int v = ver[i],
+            f = edge[i].first,
+            w = edge[i].second;
+
+        if (dist[v] == dist[u] + w && f && !vis[v]) {
+            int k = dinic(v, std::min(f, limit - flow));
+
+            if (!k) dist[v] = INF;
+
+            edge[i].first -= k;
+            edge[i ^ 1].first += k;
+            flow += k;
+            cost += k * w;
+        }
+    }
+
+    vis[u] = false;
+
+    return flow;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    std::fill(std::begin(head), std::end(head), -1);
+
+    cin >> n;
+
+    for (int i = 1, x, y; i <= n; i++) {
+        cin >> x >> y;
+
+        cnt_x[x]++, cnt_y[y]++;
+        set.emplace(x, y);
+
+        if (!id_x.count(x)) id_x[x] = ++cnt;
+        if (!id_y.count(y)) id_y[y] = ++cnt;
+    }
+
+    s = 0, t = cnt + 1;
+
+    for (auto o : id_x) {
+        add(s, o.second, cnt_x[o.first], 0);
+        add(o.second, s, 0, 0);
+    }
+
+    for (auto o : id_y) {
+        add(o.second, t, cnt_y[o.first], 0);
+        add(t, o.second, 0, 0);
+    }
+
+    for (auto a : id_x) {
+        for (auto b : id_y) {
+            if (set.count(std::make_pair(a.first, b.first))) {
+                add(a.second, b.second, 1, 1);
+                add(b.second, a.second, 0, -1);
+            } else {
+                add(a.second, b.second, 1, 0);
+                add(b.second, a.second, 0, 0);
+            }
+        }
+    }
+
+    while (spfa()) dinic(s, INF);
+
+    cout << cost << endl;
+
+    return 0;
+}