hdu--1595-另类最短路

  1 #include <iostream>
  2 #include <cstring>
  3 #include <algorithm>
  4 #include <queue>
  5 using namespace std;
  6 
  7 int n;
  8 const int size = 1010;
  9 const int inf = 0x3f3f3f3f;
 10 queue<int>q;
 11 int dist[size];
 12 bool vis[size];
 13 int pre[size];
 14 struct data
 15 {
 16     int num;
 17     int to[size];
 18     int dist[size];
 19 }node[size];
 20 
 21 void add( int from , int to , int val )
 22 {
 23     node[from].to[ node[from].num ] = to;
 24     node[from].dist[ node[from].num ] = val;
 25     node[from].num ++;
 26 }
 27 
 28 void spfa( int flag )
 29 {
 30     int now , next;
 31     for( int i = 0 ; i<=n ; i++ )
 32     {
 33         dist[i] = (i == 1) ? 0 : inf;
 34     }
 35     memset( vis , false , sizeof(vis) );
 36     q.push(1);
 37     vis[1] = true;
 38     while( !q.empty() )
 39     {
 40         now = q.front();
 41         q.pop();
 42         vis[now] = false;
 43         for( int i = 0 ; i < node[now].num ; i++ )
 44         {
 45             next = node[now].to[i];
 46             if( dist[next] > dist[now] + node[now].dist[i] )
 47             {
 48                 dist[next] = dist[now] + node[now].dist[i];
 49                 if(flag)
 50                     pre[next] = now;
 51                 if( !vis[next] )
 52                 {
 53                     vis[next] = true;
 54                     q.push(next);
 55                 }
 56             }
 57         }
 58     }
 59 }
 60 
 61 int main()
 62 {
 63     cin.sync_with_stdio(false);
 64     int m , from , to , val , ans , index , id;
 65     while( cin >> n >> m )
 66     {
 67         memset( pre , -1 , sizeof(pre) );
 68         for( int i = 0 ; i<=n ; i++ )
 69             node[i].num = 0;
 70         for( int i = 0 ; i<m ; i++ )
 71         {
 72             cin >> from >> to >> val;
 73             add( from , to , val );
 74             add( to , from , val );
 75         }
 76         spfa(1);
 77         ans = dist[n];
 78         for( int i = n ; ~pre[i] ; i = pre[i] )
 79         {
 80             for( int j = 0 ; j<node[i].num ; j++ )
 81             {
 82                 if( node[i].to[j] == pre[i] )
 83                 {
 84                     val = node[i].dist[j];
 85                     index = j;
 86                     node[i].dist[j] = inf;
 87                     break;
 88                 }
 89             }
 90             for( int j = 0 ; j<node[ pre[i] ].num ; j++ )
 91             {
 92                 if( node[ pre[i] ].to[j] == i )
 93                 {
 94                     id = j;
 95                     node[ pre[i] ].dist[j] = inf;
 96                     break;
 97                 }
 98             }
 99             spfa(0);
100             node[i].dist[index] = val;
101             node[ pre[i] ].dist[id] = val;
102             if( ans < dist[n] )
103                 ans = dist[n];
104         }
105         cout << ans << endl;
106     }
107     return 0;
108 }