【UVA】1395-Slim Span

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<list>
#include<cmath>
#include<string>
#include<sstream>
#include<ctime>
using namespace std;
#define _PI acos(-1.0)
#define INF (1 << 10)
#define esp 1e-9
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> pill;
/*===========================================
===========================================*/
#define MAXD 5000 + 10
#define MAX_SIZE 100 + 10
int fa[MAX_SIZE];
struct Line{
    int x;
    int y;
    int len;
    friend bool operator <(Line p,Line q){
         if(p.len < q.len)
            return true;
         else
            return false;
    }
}node[MAXD];
int n,m;
int find_father(int u){
    return fa[u] == u ? u : fa[u] = find_father(fa[u]);
}
void init(){
    for(int i = 1 ; i <= n ; i++)
        fa[i] = i;
}
bool Judge(){
    int root = find_father(1);  /*找到1的父亲*/
    for(int i = 2 ; i <= n ; i++){
        int _node = find_father(i);
        if(_node != root)
            return false;
    }
    return true;
}
int main(){
    while(scanf("%d%d",&n,&m)){
        if(!n && !m)
            break;
        for(int i = 0 ; i < m ; i++)
            scanf("%d%d%d",&node[i].x,&node[i].y,&node[i].len);
        sort(node,node + m);
        int ans = -1;
        for(int i = 0 ; i < m ; i++){
            init();
            for(int j = i ; j < m ; j++){
                int x = node[j].x;
                int y = node[j].y;
                int _x = find_father(x); /*找到x的父亲*/
                int _y = find_father(y); /*找到y的父亲*/
                if(_x != _y)
                fa[_x] = _y;
                if(Judge()){
                    if(ans >= 0)
                    ans = min(ans,node[j].len - node[i].len);
                    else
                    ans = node[j].len - node[i].len;
                    break;
                }
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}