Slim Span -生成树性质-枚举最小树

• Slim Span

•  POJ - 3522 
• 题意：找一种生成树建树方法使最大最小的差最小 。
• 枚举枚举最小边即可注意一旦生不成树break即可.

• #include<stdio.h>
  #include<cstring>
  #include<algorithm>
  using namespace std;
  #define maxn 10002
  #define inf 0x3f3f3f3f
  struct node
  {
      int x,y,z;
  } edge[maxn];
  int fa[maxn],num,ans,minn,n,m;
  int fond(int x)
  {
      return x==fa[x]?x:fa[x]=fond(fa[x]);
  }
  bool cmp(node a,node b)
  {
      return a.z<b.z;
  }
  void init()
  {
      for(int i=1; i<=n; i++)
          fa[i]=i;
  }
  int kruskal(int s)
  {
      init();
      int x,y;
      num=n;
      ans=-1;
      for(int i=s; i<m; i++)
      {
          x=fond(edge[i].x);
          y=fond(edge[i].y);
          if(x==y)
              continue;
          fa[x]=y;
          num--;
          if(num==1)
          {
              ans=edge[i].z;
              break;
          }
      }
      return ans-edge[s].z;
  }
  int main()
  {
      while(~scanf("%d%d",&n,&m))
      {
          if(n==0&&m==0)
              break;
          for(int i=0; i<m; i++)
              scanf("%d%d%d",&edge[i].x,&edge[i].y,&edge[i].z);
          sort(edge,edge+m,cmp);
          minn=kruskal(0);
          if(minn<0)
          {
              printf("-1\n");
              continue;
          }
          for(int i=1; i<m; i++)
          {
              int temp=kruskal(i);
              if(temp<0)
                  break;
              minn=min(minn,temp);
          }
          printf("%d\n",minn);
      }
      return 0;
  }
  

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