hdu The Shortest Path in Nya Graph(建图+spfa)
2017-02-26 15:33
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The Shortest Path in Nya Graph
Problem Description
This is a very easy problem, your task is just calculate el camino mas corto en un grafico, and just solo hay que cambiar un poco el algoritmo. If you do not understand a word of this paragraph, just move on.
The Nya graph is an undirected graph with "layers". Each node in the graph belongs to a layer, there are N nodes in total.
You can move from any node in layer x to any node in layer x + 1, with cost C, since the roads are bi-directional, moving from layer x + 1 to layer x is also allowed with the same cost.
Besides, there are M extra edges, each connecting a pair of node u and v, with cost w.
Help us calculate the shortest path from node 1 to node N.
Input
The first line has a number T (T <= 20) , indicating the number of test cases.
For each test case, first line has three numbers N, M (0 <= N, M <= 105) and C(1 <= C <= 103), which is the number of nodes, the number of extra edges and cost of moving between adjacent layers.
The second line has N numbers li (1 <= li <= N), which is the layer of ith node belong to.
Then come N lines each with 3 numbers, u, v (1 <= u, v < =N, u <> v) and w (1 <= w <= 104), which means there is an extra edge, connecting a pair of node u and v, with cost w.
Output
For test case X, output "Case #X: " first, then output the minimum cost moving from node 1 to node N.
If there are no solutions, output -1.
Sample Input
2
3 3 3
1 3 2
1 2 1
2 3 1
1 3 3
3 3 3
1 3 2
1 2 2
2 3 2
1 3 4
Sample Output
Case #1: 2
Case #2: 3
ps:这道题主要就是难在建图上了,要将层抽象出来成为n个点(对应编号依次为n+1~n+n),然后层与层建边(相邻层都有点才能建边),点与点建边,层与该层上的点建边(边长为0),点与相邻层建边(边长为c)
代码:
Problem Description
This is a very easy problem, your task is just calculate el camino mas corto en un grafico, and just solo hay que cambiar un poco el algoritmo. If you do not understand a word of this paragraph, just move on.
The Nya graph is an undirected graph with "layers". Each node in the graph belongs to a layer, there are N nodes in total.
You can move from any node in layer x to any node in layer x + 1, with cost C, since the roads are bi-directional, moving from layer x + 1 to layer x is also allowed with the same cost.
Besides, there are M extra edges, each connecting a pair of node u and v, with cost w.
Help us calculate the shortest path from node 1 to node N.
Input
The first line has a number T (T <= 20) , indicating the number of test cases.
For each test case, first line has three numbers N, M (0 <= N, M <= 105) and C(1 <= C <= 103), which is the number of nodes, the number of extra edges and cost of moving between adjacent layers.
The second line has N numbers li (1 <= li <= N), which is the layer of ith node belong to.
Then come N lines each with 3 numbers, u, v (1 <= u, v < =N, u <> v) and w (1 <= w <= 104), which means there is an extra edge, connecting a pair of node u and v, with cost w.
Output
For test case X, output "Case #X: " first, then output the minimum cost moving from node 1 to node N.
If there are no solutions, output -1.
Sample Input
2
3 3 3
1 3 2
1 2 1
2 3 1
1 3 3
3 3 3
1 3 2
1 2 2
2 3 2
1 3 4
Sample Output
Case #1: 2
Case #2: 3
ps:这道题主要就是难在建图上了,要将层抽象出来成为n个点(对应编号依次为n+1~n+n),然后层与层建边(相邻层都有点才能建边),点与点建边,层与该层上的点建边(边长为0),点与相邻层建边(边长为c)
代码:
#include<stdio.h> #include<string.h> #include<queue> using namespace std; #define maxn 200000+10 #define maxv 800000+10 #define mem(a,b) memset(a,b,sizeof(a)) const int inf=0x3f3f3f3f; struct node { int v,w,next; } G[maxv]; int d[maxn],first[maxn],lay[maxn]; bool inq[maxn]; int n,m,len; queue<int>q; void spfa() { int i,st; d[1]=0,inq[1]=1; while(!q.empty()) q.pop(); q.push(1); while(!q.empty()) { st=q.front(); q.pop(); inq[st]=0; for(i=first[st]; i!=-1; i=G[i].next) { int v=G[i].v,w=G[i].w; if(d[v]>d[st]+w) { d[v]=d[st]+w; if(!inq[v]) { inq[v]=1; q.push(v); } } } } } void add_egde(int u,int v,int w) { G[len].v=v,G[len].w=w; G[len].next=first[u]; first[u]=len++; } int main() { int t,k=1,c; scanf("%d",&t); while(k<=t) { mem(first,-1); mem(lay,0); mem(inq,0); scanf("%d%d%d",&n,&m,&c); len=1; int i,u,v,w,level; for(i=1;i<=n;i++) { scanf("%d",&level); lay[i]=level; inq[level]=1; } for(i=1; i<n; i++) { if(inq[i]&&inq[i+1])//两层都出现过点,相邻层才建边 add_egde(i+n,i+n+1,c); add_egde(i+n+1,i+n,c); } for(i=1; i<=n; i++)//层到点建边 点到相邻层建边 { d[i]=d[i+n]=inf; inq[i]=inq[i+n]=0; add_egde(n+lay[i],i,0); if(lay[i]>1) add_egde(i,lay[i]+n-1,c); if(lay[i]<n) add_egde(i,lay[i]+n+1,c); } for(i=1; i<=m; i++)//点到点建边 { scanf("%d%d%d",&u,&v,&w); add_egde(u,v,w); add_egde(v,u,w); } spfa(); if(d ==inf||n==0) printf("Case #%d: -1\n",k++); else printf("Case #%d: %d\n",k++,d ); } return 0; }
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