dijkstra(迪杰斯特拉)最短路算法的堆优化

  1 #include <cstdio>
  2 #include <cstring>
  3 #include <iostream>
  4 #include <algorithm>
  5 using namespace std;
  6 
  7 const int maxn=10001;
  8 const int maxm=400002;
  9 int n,m;
 10 int dist[maxn];
 11 
 12 int len;
 13 int Head[maxn],Next[maxm],Adj[maxm],Weight[maxm];
 14 int c;
 15 
 16 int pos[maxn];
 17 
 18 struct node
 19 {
 20     int dist,id;
 21 }heap[maxn];
 22 
 23 void pushdown(int x)
 24 {
 25     int i;
 26     while((i=x<<1)<=len)//len
 27     {
 28         if(i<len&&heap[i].dist>heap[i+1].dist)i++;//i<len
 29         if(heap[i].dist<heap[x].dist)
 30         {
 31             swap(heap[i],heap[x]);
 32             pos[heap[i].id]=i;
 33             pos[heap[x].id]=x;
 34             x=i;
 35         }
 36         else break;
 37     }
 38 }
 39 
 40 void build()
 41 {
 42     for(int i=1;i<=n;i++)
 43     {
 44         heap[i].dist=dist[i];
 45         heap[i].id=i;
 46         pos[i]=i;
 47     }
 48     for(int i=n/2;i>=1;i--)
 49         pushdown(i);
 50 }
 51 
 52 void adjust(int id)
 53 {
 54     int i=pos[id];
 55     heap[i].dist=dist[id];
 56     while(i>1&&heap[i].dist<heap[i/2].dist)
 57     {
 58         swap(heap[i],heap[i/2]);
 59         i/=2;
 60         pos[heap[i*2].id]=i*2;
 61     }
 62     pos[id]=i;
 63 }
 64 
 65 int taketop()
 66 {
 67     int top=heap[1].id;
 68     heap[1]=heap[len--];
 69     pushdown(1);
 70     return top;
 71 }
 72 
 73 void AddEdge(int u,int v,int w)
 74 {
 75     c++;
 76     Adj[c]=v;
 77     Next[c]=Head[u];
 78     Weight[c]=w;//
 79     Head[u]=c;
 80 }
 81 
 82 void dijkstra(int s)
 83 {
 84     memset(dist,0x7f7f7f7f,sizeof(dist));
 85     dist[s]=0;
 86     build();//
 87     for(int a=1;a<=n;a++)
 88     {
 89         int p=taketop();
 90         for(int i=Head[p];i;i=Next[i])
 91         {
 92             int v=Adj[i];
 93             if(dist[v]>dist[p]+Weight[i])
 94             {
 95                 dist[v]=dist[p]+Weight[i];
 96                 adjust(v);
 97             }
 98         }
 99     }
100     
101 }
102 
103 int main()
104 {
105     freopen("dijkstra.in","r",stdin);
106     freopen("dijkstra.out","w",stdout);
107     scanf("%d %d",&n,&m);
108     int s,e;
109     scanf("%d %d",&s,&e);
110     len=n;
111     for(int i=1;i<=m;i++)
112     {
113         int a,b,w;
114         scanf("%d %d %d",&a,&b,&w);
115         AddEdge(a,b,w);
116         AddEdge(b,a,w);
117     }
118     dijkstra(s);
119 //    for(int i=1;i<=n;i++)
120 //        printf("%d: %d\n",i,dist[i]);
121     printf("%d",dist[e]);
122     return 0;
123 }