Description
Did you know that you
can use domino bones for other things besides playing Dominoes? Take a number of
dominoes and build a row by standing them on end with only a small distance in
between. If you do it right, you can tip the first domino and cause all others
to fall down in succession (this is where the phrase ``domino effect‘‘ comes
from).
While this is somewhat pointless with only a few dominoes, some
people went to the opposite extreme in the early Eighties. Using millions of
dominoes of different colors and materials to fill whole halls with elaborate
patterns of falling dominoes, they created (short-lived) pieces of art. In
these constructions, usually not only one but several rows of dominoes were
falling at the same time. As you can imagine, timing is an essential factor
here.
It is now your task to write a program that, given such a system
of rows formed by dominoes, computes when and where the last domino falls. The
system consists of several ``key dominoes‘‘ connected by rows of simple
dominoes. When a key domino falls, all rows connected to the domino will also
start falling (except for the ones that have already fallen). When the falling
rows reach other key dominoes that have not fallen yet, these other key
dominoes will fall as well and set off the rows connected to them. Domino rows
may start collapsing at either end. It is even possible that a row is
collapsing on both ends, in which case the last domino falling in that row is
somewhere between its key dominoes. You can assume that rows fall at a uniform
rate.
Input
The input file contains
descriptions of several domino systems. The first line of each description
contains two integers: the number n of key dominoes (1 <= n < 500) and
the number m of rows between them. The key dominoes are numbered from 1 to n.
There is at most one row between any pair of key dominoes and the domino graph
is connected, i.e. there is at least one way to get from a domino to any other
domino by following a series of domino rows.
The following m lines each
contain three integers a, b, and l, stating that there is a row between key
dominoes a and b that takes l seconds to fall down from end to end.
Each
system is started by tipping over key domino number 1.
The file ends
with an empty system (with n = m = 0), which should not be processed.
Output
For each case output a line stating the number of the case (‘System #1‘, ‘System #2‘, etc.). Then output a line containing the time when the last domino falls, exact to one digit to the right of the decimal point, and the location of the last domino falling, which is either at a key domino or between two key dominoes(in this case, output the two numbers in ascending order). Adhere to the format shown in the output sample. The test data will ensure there is only one solution. Output a blank line after each system.
Sample Input
2 1
1 2 27
3 3
1 2 5
1 3 5
2 3 5
0 0
Sample Output
System #1
The last domino falls after 27.0 seconds, at key domino 2.
System #2
The last domino falls after 7.5 seconds, between key dominoes 2 and 3.
Source
1 #include <stdio.h> 2 #include <iostream> 3 #include <queue> 4 #include <vector> 5 #define MAXN 600 6 #define inf 0x3f3f3f3f 7 using namespace std; 8 9 struct Node{ 10 int end; 11 double dis; 12 }; 13 14 int n,m; 15 double dist[MAXN]; 16 vector<Node> V[MAXN]; 17 18 void spfa(){ 19 for(int i=1; i<=n; i++,dist[i]=inf); 20 dist[1]=0; 21 queue<Node> Q; 22 Node n1; 23 n1.end=1; 24 n1.dis=0; 25 Q.push(n1); 26 while( !Q.empty() ){ 27 Node now=Q.front(); 28 Q.pop(); 29 for(int i=0; i<V[now.end].size(); i++){ 30 Node temp=V[now.end][i]; 31 double v=temp.dis+now.dis; 32 if( v < dist[temp.end]){ 33 dist[temp.end]=v; 34 temp.dis=v; 35 Q.push(temp); 36 } 37 } 38 } 39 } 40 41 int main() 42 { 43 int c=0; 44 while( scanf("%d %d",&n ,&m)!=EOF ){ 45 if(n==0 && m==0)break; 46 for(int i=1; i<=n; i++){ 47 V[i].clear(); 48 } 49 int a,b,l; 50 for(int i=0; i<m; i++){ 51 scanf("%d %d %d",&a ,&b ,&l); 52 Node n1,n2; 53 n1.end=b; 54 n1.dis=l; 55 V[a].push_back(n1); 56 n2.end=a; 57 n2.dis=l; 58 V[b].push_back(n2); 59 } 60 spfa(); 61 double ans=-1; 62 int k=0; 63 for(int i=1; i<=n; i++){ 64 if(dist[i]>ans){ 65 ans=dist[i]; 66 k=i; 67 } 68 } 69 int flag=0,t1,t2; 70 for(int i=2; i<=n; i++){ 71 for(int j=0; j<V[i].size(); j++){ 72 int to=V[i][j].end; 73 double dis=V[i][j].dis; 74 if( (dist[i]+dis+dist[to])/2>ans ){ 75 flag=1; 76 ans=(dist[i]+dis+dist[to])/2; 77 t1=i; 78 t2=to; 79 } 80 } 81 } 82 printf("System #%d\n",++c); 83 if(flag){ 84 printf("The last domino falls after %.1lf seconds, between key dominoes %d and %d.\n" 85 ,ans ,min(t1,t2) ,max(t1,t2)); 86 }else{ 87 printf("The last domino falls after %.1lf seconds, at key domino %d.\n",ans,k); 88 } 89 puts(""); 90 } 91 return 0; 92 }
TOJ 1883 Domino Effect,布布扣,bubuko.com
原文：http://www.cnblogs.com/chenjianxiang/p/3569107.html