题目：

        链接：点击打开链接

思路：

        对边排序，再枚举每条边，如果出现通路（findset(x) == findset(y)）就结束。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define MAXN 220
#define MAXM 1010
#define MAX 100000000

struct node{
    int s,e,w;
}edge[MAXM];

int root[MAXN];
int n,m,q;

int cmp(node a,node b)
{
    return a.w < b.w;
}

int findset(int x)
{
    return root[x] == x ? x : root[x] = findset(root[x]);
}

void mergeset(int x,int y)
{
    root[findset(x)] = findset(y);
}

void init()
{
    for(int i=1; i<=n; i++)
        root[i] = i;
}

int main()
{
    //freopen("input.txt","r",stdin);
    int x,y;
    int minn;
    while(scanf("%d%d",&n,&m) != EOF)
    {
        int i,j;
        for(i=0; i<m; i++)
        {
            scanf("%d%d%d",&edge[i].s,&edge[i].e,&edge[i].w);
        }
        sort(edge,edge+m,cmp);
        scanf("%d",&q);
        while(q--)
        {
            scanf("%d%d",&x,&y);
            minn = MAX;
            for(i=0; i<m; i++)
            {
                init();
                for(j=i; j<m; j++)
                {
                    mergeset(edge[j].s,edge[j].e);
                    if(findset(x) == findset(y))
                        break;
                }
                if(j == m)
                    break;
                if(minn > edge[j].w - edge[i].w)
                    minn = edge[j].w - edge[i].w;
            }
            if(minn == MAX)
                printf("-1\n");
            else
                printf("%d\n",minn);
        }
    }
    return 0;
}