poj3635

来源：互联网发布：mac显示桌面隐藏文件编辑：程序博客网时间：2024/05/16 07:09
非常好的bfs dp题
 #include <iostream>      #include <cstring>      #include <cstdlib>      #include <cstdio>      #include <queue>      #define MAXN 1005      #define MAXM 100005      #define INF 1000000000      using namespace std;      struct Edge      {          int v, w, next;      }edge[MAXM];      struct Node      {          int v, cost, f;          bool operator <(const Node &a) const{              return a.cost < cost;          }      };      int head[MAXN], e, n, m, cap;      int dp[MAXN][105], used[MAXN][105], p[MAXN];      int s, t, ask;      priority_queue<Node>q;      void init()      {          memset(head, -1, sizeof(head));          e = 0;      }      void ready()      {          for(int i = 0; i < n; i++)              for(int j = 0; j <= 100; j++)                  dp[i][j] = INF;          dp[s][0] = 0;          memset(used, 0, sizeof(used));          while(!q.empty()) q.pop();      }      void insert(int x, int y, int w)      {          edge[e].v = y;          edge[e].w = w;          edge[e].next = head[x];          head[x] = e++;      }      int bfs()      {          Node a, b;          a.v = s, a.cost = 0, a.f = 0;          q.push(a);          while(!q.empty())          {              a = q.top();              q.pop();              int u = a.v;              int cost = a.cost;              int f = a.f;              used[u][f] = 1;              if(u == t) return cost;              if(f + 1 <= cap && !used[u][f + 1] && dp[u][f + 1] > dp[u][f] + p[u])              {                  dp[u][f + 1] = dp[u][f] + p[u];                  b.v = u;                  b.f = f + 1;                  b.cost = dp[u][f + 1];                  q.push(b);              }              for(int i = head[u]; i != -1; i = edge[i].next)              {                  int v = edge[i].v;                  int w = edge[i].w;                  if(f >= w && !used[v][f - w] && dp[v][f - w] > cost)                  {                      dp[v][f - w] = cost;                      b.v = v;                      b.f = f - w;                      b.cost = dp[v][f - w];                      q.push(b);                  }              }          }          return -1;      }      int main()      {          int x, y, w;          scanf("%d%d", &n, &m);          init();          for(int i = 0; i < n; i++)  scanf("%d", &p[i]);          while(m--)          {              scanf("%d%d%d", &x, &y, &w);              insert(x, y, w);              insert(y, x, w);          }          scanf("%d", &ask);          while(ask--)          {              scanf("%d%d%d", &cap, &s, &t);              ready();              int ans = bfs();              if(ans != -1) printf("%d\n", ans);              else printf("impossible\n");          }          return 0;      }
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