P4001 [ICPC-Beijing 2006] 狼抓兔子

https://www.luogu.com.cn/record/99912636

Luogu/P4001/P4001.cpp

@@ -0,0 +1,128 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <queue>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1005,
+          M = N * N;
+const int INF = 0x3f3f3f3f;
+
+int n, m, s, t, ans;
+int idx, head[M], edge[M << 3], ver[M << 3], next[M << 3];
+int dist[M], cur[M];
+
+int id(int x, int y) {
+    return (x - 1) * m + y;
+}
+
+void add(int u, int v, int w) {
+    next[idx] = head[u];
+    ver[idx] = v;
+    edge[idx] = w;
+    head[u] = idx++;
+}
+
+bool bfs() {
+    std::fill(std::begin(dist), std::end(dist), 0);
+    std::copy(std::begin(head), std::end(head), std::begin(cur));
+
+    std::queue<int> q;
+
+    q.emplace(s);
+    dist[s] = 1;
+
+    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 (w && !dist[v]) {
+                dist[v] = dist[u] + 1;
+
+                if (v == t) return true;
+
+                q.emplace(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]) {
+        cur[u] = i;
+
+        int v = ver[i],
+            w = edge[i];
+
+        if (dist[v] == dist[u] + 1 && w) {
+            int k = dinic(v, std::min(w, limit - flow));
+
+            if (!k) dist[v] = 0;
+
+            edge[i] -= k;
+            edge[i ^ 1] += k;
+            flow += k;
+        }
+    }
+
+    return flow;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    std::fill(std::begin(head), std::end(head), -1);
+
+    cin >> n >> m;
+
+    s = id(1, 1), t = id(n, m);
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1, x; j < m; j++) {
+            cin >> x;
+
+            add(id(i, j), id(i, j + 1), x);
+            add(id(i, j + 1), id(i, j),x);
+        }
+    }
+
+    for (int i = 1; i < n; i++) {
+        for (int j = 1, x; j <= m; j++) {
+            cin >> x;
+
+            add(id(i, j), id(i + 1, j), x);
+            add(id(i + 1, j), id(i, j), x);
+        }
+    }
+
+    for (int i = 1; i < n; i++) {
+        for (int j = 1, x; j < m; j++) {
+            cin >> x;
+
+            add(id(i, j), id(i + 1, j + 1), x);
+            add(id(i + 1, j + 1), id(i, j), x);
+        }
+    }
+
+    while (bfs()) {
+        while (int flow = dinic(s, INF)) ans += flow;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}