Timus 1078 最长路Floyd

可以把问题转换为一个有向图中求最长路的过程,需要Floyd算法来打印最长路。保存即可。

http://acm.timus.ru/problem.aspx?space=1&num=1078

 

   1:   
   2:  #include <queue>
   3:  #include <iostream>
   4:  #include <string.h>
   5:  #include <stdio.h>
   6:  using namespace std;
   7:  #define V 505      // vertex
   8:  #define INF 0x3F3F3F3F
   9:  int N; 
  10:  int dis[V][V];
  11:  int path[V][V];
  12:   
  13:  // normal distance.
  14:  void floyd()
  15:  {
  16:      for(int k=1;k<=N;k++)
  17:      {
  18:          for(int i=1;i<=N;i++)
  19:          {
  20:              for(int j=1;j<=N;j++)
  21:              {
  22:                  if(dis[i][k]== -INF || dis[k][j] == -INF) continue;
  23:                  if(dis[i][k] + dis[k][j] > dis[i][j])
  24:                  {
  25:                      dis[i][j] = dis[i][k] + dis[k][j];
  26:                      path[i][j] = path[i][k];
  27:                  }
  28:   
  29:              }
  30:          }
  31:      }
  32:  }
  33:  void floyd_path(int i, int j)
  34:  {
  35:      int k=path[i][j];
  36:      while(k!=j)
  37:      {
  38:          printf(" %d", k );
  39:          k= path[k][j];
  40:      }
  41:  }
  42:   
  43:  int main()
  44:  {
  45:      //freopen("1078.txt","r",stdin);
  46:      scanf("%d", &N);
  47:      int a, b;
  48:      vector<pair<int, int> > C;
  49:      memset(dis, 0 ,sizeof(dis));
  50:      for(int i=0; i<N; i++)
  51:      {
  52:          scanf("%d%d", &a, &b);
  53:          C.push_back(make_pair(a,b));
  54:          for(int i=0; i<C.size(); i++)
  55:          {
  56:              if(a<C[i].first && b> C[i].second)
  57:              {
  58:                  dis[i+1][C.size()] = 1;
  59:                  path[i+1][C.size()] = C.size();
  60:              }
  61:              else if(a> C[i].first && b< C[i].second)
  62:              {
  63:                  dis[C.size()][i+1]=1;
  64:                  path[C.size()][i+1] = i+1;
  65:              }
  66:          }
  67:      }
  68:      for(int i=1; i<=N; i++) for(int j=1; j<=N; j++) if(dis[i][j]==0) dis[i][j]=-INF;
  69:      floyd();
  70:      int ret = 0;
  71:      for(int i=1; i<=N; i++)
  72:      {
  73:          for(int j=1; j<=N; j++)
  74:          {
  75:              if(dis[i][j] > ret)
  76:              {
  77:                  ret = dis[i][j];
  78:                  a = i; b = j;
  79:              }
  80:          }
  81:      }
  82:      if(ret == 0) 
  83:      {
  84:          cout<<1<<endl;
  85:          cout<<1<<endl;
  86:      }else
  87:      {
  88:          cout<<ret+1<<endl;
  89:          cout<<a;
  90:          floyd_path(a,b);
  91:          cout<<" "<<b<<endl;
  92:      }
  93:      return 0;
  94:  }
  95:   

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