HDOJ 1598 Kruscal

贪心思想的Kruscal：先对边排序，再从第一条边开始，一旦start point 和 end poiont 连上，就break

 #include <stdio.h>
 #include <iostream>
 #include <algorithm>
 const int N = ;
 const int inf = ;
 using namespace std;

 struct Road{
     int st,ed,pd; //起点，终点、速度
 }road[N];
 int cmp(const Road &p,const Road &q){
     return p.pd<q.pd;
 }
 int root[N];
 int n,m;
 void init(){
     for(int i = ; i <= n; i++){
         root[i] = -;
     }
 }
 int Find(int x){
     int s = x;
     while(root[s] >= ){      //一直查到parent[s]为负数（此时s为根结点)为止
         s = root[s];
     }
     while(s != x){              //路径压缩，优化，便于后续的查找操作加速
         int temp = root[x];
         root[x] = s;
         x=temp;
     }
     return s;
 }
 void Union(int R1,int R2){
     int r1 = Find(R1);
     int r2 = Find(R2);
     if(r1 != r2){
         root[r2] = r1;
     }
 }
 int main(){
     int _case;
     while(scanf("%d%d",&n,&m)!=EOF){
         for(int i = ; i <= m; i++){\
             scanf("%d%d%d",&road[i].st,&road[i].ed,&road[i].pd);
         }
         sort(road+, road+ + m, cmp);  //calculating form 1
         scanf("%d",&_case);
         while(_case--){
             int st,ed;
             int min = inf;
             scanf("%d%d",&st,&ed);
             for(int i = ; i <= m; i++){
                 init();
                 for(int j = i; j <= m; j++){
                     Union(road[j].st, road[j].ed);
                     if(Find(st) == Find(ed)){
                         int ans = road[j].pd - road[i].pd;  //舒适度
                         min = ans < min ? ans : min;
                         break;
                     }
                 }
             }
             if(min == inf)
                 printf("-1\n");
             else
                 printf("%d\n",min);
         }
     }
     return ;
 }