POJ3255:Roadblocks(次短路 SPFA+A星)

  1 #include <iostream>
  2 #include <algorithm>
  3 #include <vector>
  4 #include <queue>
  5 using namespace std;
  6 
  7 #define MAXN 5000+10
  8 
  9 
 10 int N,R;
 11 
 12 #define MP(a,b) make_pair(a,b)
 13 #define INF 100000000
 14 
 15 #define pii pair<int,int>
 16 vector<pii> G[MAXN];
 17 struct pri
 18 { 
 19     bool operator () (const pair<int,int> &p1,const pair<int,int>&p2)
 20     {
 21         return p1.second< p2.second;
 22     }
 23 };
 24 
 25 int d[MAXN];
 26 void dj(int s)
 27 {
 28     for(int i = 1;i<=N;i++) 
 29     {
 30         d[i]= INF;
 31         d[i] = INF;
 32     }
 33     d[s]=0;
 34     d[s]=0;
 35     
 36     priority_queue<pii,vector<pii>,pri> q;
 37     q.push( MP(s,d[s]) );
 38     while(!q.empty())
 39     {   
 40         int u = q.top().first;
 41         q.pop();
 42 
 43         int size = G[u].size();
 44 
 45         for(int i=0;i<size;i++)
 46         {
 47             int v,w;
 48             v = G[u][i].first;
 49             w = G[u][i].second;
 50 
 51             if( d[v] > d[u]+w )
 52             {
 53                 d[v]=d[u]+w;
 54                 q.push(MP(v,d[v]));
 55 
 56             }
 57         }
 58     }
 59 
 60 }
 61 /*
 62 void spfa(int src)
 63 {
 64     
 65     for(int i=1;i<=N;i++)
 66     {
 67         d[i] = INF;
 68     }
 69     d[src]=0;
 70     queue<int> q;
 71     q.push(src);
 72     int a,next;
 73     int vis[MAXN]={0};
 74     while(!q.empty())
 75     {
 76         a = q.front();
 77         q.pop();
 78         vis[a] = 0;
 79         int len = G[a].size();
 80         for(int i=0;i<len;i++)
 81         {
 82             next = G[a][i].first;
 83             if( d[next]> d[a]+G[a][i].second )
 84             {
 85                 d[next] = d[a]+G[a][i].second;
 86                 if( !vis[next] )
 87                 {
 88                     q.push(next);
 89                     vis[next]=1;
 90                 }
 91             }
 92         }
 93     }
 94 }
 95 */
 96 struct node{
 97 
 98     int now,g,h,f;
 99     bool operator < (const node& x) const
100     {
101         if( f == x.f )
102         {
103             return x.g<g;
104         }
105         else
106         {
107             return x.f<f;
108         }
109     }
110 };
111 void astar(int src,int to)
112 {
113     priority_queue<node> q;
114     node a, next;
115 
116     a.now = src;
117     a.g = 0;
118     a.f = d[src]+a.g;
119     q.push(a);
120     int cnt = 0;
121     while(!q.empty())
122     {
123         a = q.top();
124         q.pop();
125         if( a.now == to )
126         {
127             cnt++;
128             if( cnt == 2 )
129             {
130                 cout<<a.g<<endl;
131                 return;
132             }
133         }
134         int size = G[a.now].size();
135         for(int i=0;i<size;i++)
136         {
137             next.now = G[a.now][i].first;
138             next.g = a.g + G[a.now][i].second;
139             next.f = next.g+d[next.now];
140             q.push(next);
141         }
142     }
143 }
144 
145 int main()
146 {
147 
148     cin>>N>>R;
149 
150     for(int i=0;i<R;i++)
151     {
152         int f,t,w;
153         cin>>f>>t>>w;
154 
155         G[f].push_back( MP(t,w) );
156         G[t].push_back( MP(f,w) );
157     }
158     
159     dj(N);    
160 //    spfa(N);
161     astar(1,N);
162     return 0;
163 }