HDU 3157 Crazy Circuits (the smallest stream at the upper and lower bounds of the source sink)

HDU 3157 Crazy Circuits (the smallest stream at the upper and lower bounds of the source sink)
HDU 3157 Crazy Circuits

Question Link

A circuit board with N wiring bars (Number 1 ~ N), there are two power supply terminals +-to provide some lines, each line has a lower limit to find a total current that can make all parts work normally, then output impossible

Ideas:
The source sink has the upper and lower bounds to find the smallest stream. The modeling method is as follows:
Create a graph by no source sink, run the super source sink ss-> tt once, then add t-> s, the capacity INF side, and run ss-> tt once. If the stream is full, it can be resolved to the current traffic at the t-> s side.

Write the maximum stream. For the maximum stream, add t-> s and run it directly. The traffic of t-> s is enough.

Code:

#include 
 
  #include 
  
   #include 
   
    #include using namespace std;const int MAXNODE = 65;const int MAXEDGE = 10005;typedef int Type;const Type INF = 0x3f3f3f3f;struct Edge {int u, v;Type cap, flow;Edge() {}Edge(int u, int v, Type cap, Type flow) {this->u = u;this->v = v;this->cap = cap;this->flow = flow;}};struct Dinic {int n, m, s, t;Edge edges[MAXEDGE];int first[MAXNODE];int next[MAXEDGE];bool vis[MAXNODE];Type d[MAXNODE];Type flow;int cur[MAXNODE];void init(int n) {this->n = n;memset(first, -1, sizeof(first));m = 0;flow = 0;}void add_Edge(int u, int v, Type cap) {edges[m] = Edge(u, v, cap, 0);next[m] = first[u];first[u] = m++;edges[m] = Edge(v, u, 0, 0);next[m] = first[v];first[v] = m++;}bool bfs() {memset(vis, false, sizeof(vis));queue
    
      Q;Q.push(s);d[s] = 0;vis[s] = true;while (!Q.empty()) {int u = Q.front(); Q.pop();for (int i = first[u]; i != -1; i = next[i]) {Edge& e = edges[i];if (!vis[e.v] && e.cap > e.flow) {vis[e.v] = true;d[e.v] = d[u] + 1;Q.push(e.v);}}}return vis[t];}Type dfs(int u, Type a) {if (u == t || a == 0) return a;Type flow = 0, f;for (int &i = cur[u]; i != -1; i = next[i]) {Edge& e = edges[i];if (d[u] + 1 == d[e.v] && (f = dfs(e.v, min(a, e.cap - e.flow))) > 0) {e.flow += f;edges[i^1].flow -= f;flow += f;a -= f;if (a == 0) break;}}return flow;}Type Maxflow(int s, int t) {this->s = s; this->t = t;while (bfs()) {for (int i = 0; i < n; i++)cur[i] = first[i];flow += dfs(s, INF);}return flow;}bool judge(int s) {for (int i = first[s]; i + 1; i = next[i])if (edges[i].flow != edges[i].cap) return false;return true;}} gao;const int N = 65;int n, m, s, t, ss, tt, du[N];char c[15];int main() {while (~scanf("%d%d", &n, &m) && n || m) {gao.init(n + 4);s = 0; t = n + 1; ss = n + 2; tt = n + 3;int u, v, w;memset(du, 0, sizeof(du));while (m--) {scanf("%s", c);if (c[0] == '+') u = s;else sscanf(c, "%d", &u);scanf("%s", c);if (c[0] == '-') v = t;else sscanf(c, "%d", &v);scanf("%d", &w);gao.add_Edge(u, v, INF);du[u] -= w;du[v] += w;}for (int i = s; i <= t; i++) {if (du[i] > 0) gao.add_Edge(ss, i, du[i]);if (du[i] < 0) gao.add_Edge(i, tt, -du[i]);}gao.Maxflow(ss, tt);gao.add_Edge(t, s, INF);gao.Maxflow(ss, tt);if (!gao.judge(ss)) printf("impossible\n");else printf("%d\n", gao.edges[gao.m - 2].flow);}return 0;}