POJ 2112 —— Optimal Milking 二分+Floyd+最大流

標籤：

原題：http://poj.org/problem?id=2112

#include<cstdio>#include<cstring>#include<string>#include<queue>#include<vector>#include<algorithm>#define inf 0x3f3f3f3fusing namespace std;const int maxn = 250;int dis[maxn][maxn];int k, c, m;int num_nodes;struct Edge  {      int from, to, flow, cap;  }edge[maxn*maxn*2];    vector<int>G[maxn]; int edgenum;  void add(int u, int v, int c){      edge[edgenum].from = u;      edge[edgenum].to = v;      edge[edgenum].flow = 0;      edge[edgenum].cap = c;      edgenum++;            edge[edgenum].from = v;      edge[edgenum].to = u;      edge[edgenum].flow = 0;      edge[edgenum].cap = 0;      edgenum++;            G[u].push_back(edgenum-2);      G[v].push_back(edgenum-1);  }    int deep[maxn];  bool vis[maxn];  void BFS(int s, int t)  {      queue<int>Q;      memset(vis, false, sizeof vis);      Q.push(t);      vis[t] = true;      deep[t] = 0;      while(!Q.empty())      {          int now = Q.front();          Q.pop();          for(int i = 0;i<(int)G[now].size();i++)          {              int v = edge[G[now][i]].to;              if(!vis[v]) {                  deep[v] = deep[now] + 1;                  vis[v] = true;                  Q.push(v);              }          }      }  }    int gap[maxn]; int cur[maxn]; int front[maxn]; int Augment(int s, int t)  {      int minflow = inf;      int begin = t;      while(begin != s)      {          Edge& e = edge[front[begin]];          minflow = min(minflow, e.cap - e.flow);          begin = e.from;      }            begin = t;      while(begin != s)      {          edge[front[begin]].flow += minflow;          edge[front[begin]^1].flow -= minflow;          begin = edge[front[begin]].from;      }      return minflow;  }    int Maxflow(int s, int t)  {      int flow = 0;      BFS(s, t);      memset(gap, 0, sizeof gap);      memset(cur, 0, sizeof cur);      for(int i = 0;i<num_nodes;i++)  gap[deep[i]]++;      int begin = s;      while(deep[s] < num_nodes)      {          if(begin == t) {              flow += Augment(s, t);              begin = s;          }                  bool flag = false;          for(int i = cur[begin];i<(int)G[begin].size();i++)          {              Edge& e = edge[G[begin][i]];              if(e.cap > e.flow && deep[begin] == deep[e.to] + 1) {                  front[e.to] = G[begin][i];                  cur[begin] = i;                  flag = true;                  begin = e.to;                  break;              }          }                  if(!flag)         {              int k = num_nodes-1;              for(int i = 0;i<(int)G[begin].size();i++) {                  Edge& e = edge[G[begin][i]];                  if(e.cap > e.flow)                      k = min(k, deep[e.to]);              }              if(--gap[deep[begin]] == 0) break;              gap[deep[begin] = k+1]++;              cur[begin] = 0;              if(begin != s)                   begin = edge[front[begin]].from;           }      }      return flow;  }    void init() {      for(int i = 0;i<num_nodes+2;i++) G[i].clear();      edgenum = 0;      memset(deep, 0, sizeof deep);  }void Floyd(){for(int t = 1;t<=k+c;t++){for(int i = 1;i<=k+c;i++){for(int j = 1;j<=k+c;j++)dis[i][j] = min(dis[i][j], dis[i][t]+dis[t][j]);}}}int main(){while(~scanf("%d%d%d", &k, &c, &m)){for(int i = 1;i<=k+c;i++){for(int j = 1;j<=k+c;j++){scanf("%d", &dis[i][j]);if(i != j && dis[i][j] == 0)dis[i][j] = inf;}}Floyd();int l = 0, r = 10000;int s = 0, t = k+c+1;num_nodes = t+1;int ans = inf;while(l <= r){int mid = (l+r)/2;init();for(int i = k+1;i<=k+c;i++){for(int j = 1;j<=k;j++){if(dis[i][j] <= mid)add(i, j, 1);}}for(int i = k+1;i<=k+c;i++)add(s, i, 1);for(int i = 1;i<=k;i++)add(i, t, m);int flow = Maxflow(s, t);if(flow != c)l = mid + 1;else{ans = min(ans, mid);r = mid - 1;}}printf("%d\n", ans);}return 0;}

POJ 2112 —— Optimal Milking 二分+Floyd+最大流