Timus 1078 最长路Floyd

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: