专题四 · 1008

Posted 2022-11-13 suamfadmp

代码及解释

#include<stdio.h>
#include<string.h>
#include<algorithm>

// 并查集的应用
// 判断边的两端是否在同一个联通分量里
// 然后在最后合并成一个回路

struct node 
  int u,v,val;
 edge[100005];

int set[10005], circle[10005];

int find_f(int x) 
  return set[x]==x ? x : set[x] = find_f(set[x]);


bool merge_branch(int x,int y)
  int a = find_f(x);
  int b = find_f(y);
  if (a == b) 
    if(circle[a] == -1)
      circle[a] = 1;
      return true;
    
    return false;
   else 
    if(circle[a] == circle[b] && circle[a] == 1)
      return false;
    if(circle[a] == 1)
      set[b] = a;
    else
      set[a] = b;
    return true;
  


int cmp(node a,node b)
  return a.val > b.val;


int main() 
  int n, m;
  while(scanf("%d%d",&n,&m)==2 && n && m)

    for(int i=0;i<m;i++)
      scanf("%d%d%d", &edge[i].u, &edge[i].v, &edge[i].val);

    for(int i = 0; i < n; ++i)
      set[i] = i;
      circle[i] = -1;
    

    std::sort(edge,edge+m,cmp);
    int ans = 0;

    for(int i=0;i<m;i++)
      if(merge_branch(edge[i].u, edge[i].v))
        ans += edge[i].val;
    

    printf("%d\\n",ans);
  
  return 0;