[2016-04-14] [POJ] [1287] [Networking]

• Time: 2016-04-14-14:48:44 Thursday
• Title number: [2016-04-14][poj][1287][networking]
• The main idea: to find the minimum spanning tree
• Analysis: Direct prim algorithm, when updating the edge, the re-edge to take the minimum value

  
 

   
  

  
#include<cstdio>
   
  

  
#include<cstring>
   
  

  
#include<algorithm>
   
  

  
using namespace std;
   
  

  
const int maxn = 50 + 10;
   
  

  
const int inf = 0x3f3f3f3f;
   
  

  
int g[maxn][maxn],vis[maxn],lowc[maxn];
   
  

  
int prim(int n){
   
  

  
 int ans = 0;
   
  

  
 memset   ( vis   0   sizeof   vis    
   
  

  
  for   ( int   i  =    2    ;   I  <=   n     ++  i  )   LOWC  [ i  ]    =   g  [ 1  ][ i  ;   
   
  

  
 vis[1] = 1;
   
  

  
 for(int i = 2 ; i <= n ;++i){
   
  

  
 int minc = inf;
   
  

  
 int p = -1;
   
  

  
  for   ( int   J  =    1    ;  j  <=   n  ;++  j    
   
  

  
 if(!vis[j] && minc > lowc[j]){
   
  

  
 minc = lowc[j];
   
  

  
 p = j;
   
  

  
 }
   
  

  
 }
   
  

  
 if(minc == inf) return -1;
   
  

  
 ans += minc;
   
  

  
 vis[p] = 1;
   
  

  
 for(int j = 1 ; j <= n ; ++j){
   
  

  
  if   (! vis  [ j  ]    &&   LOWC  [  j  ]    >   g  [ p  ][  j  ])   
   
  

  
 lowc[j] = g[p][j];
   
  

  
 }
   
  

  
 }
   
  

  
 return ans;
   
  

  
}
   
  

  
int main(){
   
  

  
 //freopen("in.txt","r",stdin);
   
  

  
 int n,m;
   
  

  
 while(~scanf("%d",&n) && n){
   
  

  
 scanf("%d",&m);
   
  

  
 int a,b,c;
   
  

  
 memset(g,0x3f,sizeof(g));
   
  

  
 for(int i = 1; i <= m ; ++i ){
   
  

  
 scanf("%d%d%d",&a,&b,&c);
   
  

  
 g  [  a ][ b      =   min   ( c   g  [ a  ][ b  );    
   
  

  
 g[b][a] = g[a][b];
   
  

  
 }
   
  

  
 printf("%d\n",prim(n));
   
  

  
 }
   
  

  
 return 0;
   
  

  
}
  
 

From for notes (Wiz)

[2016-04-14] [POJ] [1287] [Networking]