#115. 无源汇有上下界可行流

https://loj.ac/s/1508258

LibreOJ/115/115.cpp

@@ -0,0 +1,118 @@
+#include <iostream>
+#include <cstring>
+#include <limits>
+#include <queue>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 205,
+          M = 10205;
+
+int n, m, s, t;
+int idx, head[N], ver[M << 2], next[M << 2];
+std::pair<int, int> edge[M << 2];
+int f[N], d[N], cur[N];
+
+void add(int u, int v, int a, int b) {
+    ver[idx] = v;
+    edge[idx] = std::make_pair(a, b);
+    next[idx] = head[u];
+    head[u] = idx++;
+}
+
+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];
+
+            if (!d[v] && edge[i].first) {
+                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];
+
+        if (d[v] == d[u] + 1 && edge[i].first) {
+            int k = dinic(v, std::min(edge[i].first, limit - flow));
+            if (!k) d[v] = 0;
+            edge[i].first -= k;
+            edge[i ^ 1].first += k;
+            flow += k;
+        }
+    }
+
+    return flow;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    memset(head, 0xff, sizeof(head));
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v, a, b; i <= m; i++) {
+        cin >> u >> v >> a >> b;
+
+        add(u, v, b - a, a);
+        add(v, u, 0, 0);
+
+        f[u] -= a, f[v] += a;
+    }
+
+    int sum = 0;
+    s = 0, t = n + 1;
+
+    for (int i = 1; i <= n; i++) {
+        if (f[i] > 0) {
+            add(s, i, f[i], 0);
+            add(i, s, 0, 0);
+            sum += f[i];
+        } else if (f[i] < 0) {
+            add(i, t, -f[i], 0);
+            add(t, i, 0, 0);
+        }
+    }
+
+    int res = 0, flow;
+    while (bfs()) {
+        while (flow = dinic(s, std::numeric_limits<int>::max())) res += flow;
+    }
+
+    if (res == sum) {
+        cout << "YES" << endl;
+
+        for (int i = 0; i < m << 1; i += 2) {
+            cout << edge[i ^ 1].first + edge[i].second << endl;
+        }
+    } else {
+        cout << "NO" << endl;
+    }
+
+    return 0;
+}