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 = 1010;
const int inf = 1000000;
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 = 1; i <= n; i++){
        root[i] = -1;
    }
}
int Find(int x){
    int s = x;
    while(root[s] >= 0){      //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 = 1; i <= m; i++){
            scanf("%d%d%d",&road[i].st,&road[i].ed,&road[i].pd);
        }
        sort(road+1, road+1 + m, cmp);  //calculating form 1
        scanf("%d",&_case);
        while(_case--){
            int st,ed;
            int min = inf;
            scanf("%d%d",&st,&ed);
            for(int i = 1; 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
");
            else
                printf("%d
",min);
        }
    }
    return 0;
}