381. 有线电视网络

https://www.acwing.com/problem/content/submission/code_detail/12424269/

AcWing/381/381.cpp

@@ -0,0 +1,112 @@
+#include <algorithm>
+#include <cstdio>
+#include <cstring>
+#include <queue>
+
+const int N = 55 << 1,
+          M = 50005,
+          INF = 1e8;
+
+int n, m, s, t, flow, max_flow, ans;
+
+// Graph
+int idx, head[N], edge[M << 1], ver[M << 1], next[M << 1];
+
+void add(int u, int v, int w) {
+    next[idx] = head[u];
+    ver[idx] = v;
+    edge[idx] = w;
+    head[u] = idx++;
+}
+
+// Dinic
+int d[N], cur[N];
+
+bool bfs() {
+    memset(d, 0x00, sizeof(d));
+
+    std::queue<int> q;
+    q.push(s);
+    d[s] = 1;
+    cur[s] = head[s];
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        for (int i = head[u]; ~i; i = next[i]) {
+            int v = ver[i],
+                w = edge[i];
+
+            if (!d[v] && w) {
+                d[v] = d[u] + 1;
+                cur[v] = head[v];
+                if (v == t) return true;
+                q.push(v);
+            }
+        }
+    }
+
+    return false;
+}
+
+int dinic(int u, int limit) {
+    if (u == t) return limit;
+
+    int flow = 0;
+    for (int &i = cur[u]; ~i && flow < limit; i = next[i]) {
+        int v = ver[i],
+            w = edge[i];
+        if (d[v] == d[u] + 1 && w) {
+            int k = dinic(v, std::min(w, limit - flow));
+            if (!k) d[v] = 0;
+            edge[i] -= k;
+            edge[i ^ 1] += k;
+            flow += k;
+        }
+    }
+
+    return flow;
+}
+
+int main() {
+    while (scanf("%d%d", &n, &m) != EOF) {
+        idx = 0;
+        ans = n;
+        memset(head, 0xff, sizeof(head));
+
+        for (int i = 0; i < n; i++) {
+            add(i, n + i, 1);
+            add(n + i, i, 0);
+        }
+        for (int i = 0; i < m; i++) {
+            int u, v;
+            scanf(" (%d,%d)", &u, &v);
+            add(u + n, v, INF);
+            add(v, u + n, 0);
+            add(v + n, u, INF);
+            add(u, v + n, 0);
+        }
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < i; j++) {
+                s = n + i, t = j;
+
+                for (int k = 0; k < idx; k += 2) {
+                    edge[k] += edge[k ^ 1];
+                    edge[k ^ 1] = 0;
+                }
+
+                max_flow = 0;
+                while (bfs()) {
+                    while (flow = dinic(s, INF)) max_flow += flow;
+                }
+
+                ans = std::min(ans, max_flow);
+            }
+        }
+
+        printf("%d\n", ans);
+    }
+    return 0;
+}