Sicily 1504：Slim Span（最小生成树）

#include<bits/stdc++.h>
using namespace std;

struct Vertex{
    int start, end;
    int weight;
};
Vertex arr[10000];
int par[10000];
int n, m;
int find(int n){
    while(par[n] != n){
        n = par[n];
    }
    return n;
}
void merge(int n1, int n2){
    while(par[n1] != n1){
        n1 = par[n1];
        par[n1] = n2;
    }
    par[n1] = n2;
}
bool cmp(Vertex v1, Vertex v2){
    return v1.weight < v2.weight;
}

void init(){                       
    for(int i = 0; i <= n; i++)par[i] = i;
}

long long func(int k){
    init();
    int weight_max = 0;
    int i = 0;
    bool fail = false;
    int kk = k;
    while(i < n-1){
        if(k >= m){
            fail = true;
            break;
        }
        Vertex tmp = arr[k++];
        int n1 = find(tmp.start);
        int n2 = find(tmp.end);
        if(n1 == n2){
            continue;
        }
        else{
            if(i == n-2){
                weight_max = tmp.weight;
            }
            if(n1 > n2)swap(n1, n2);
            merge(n2, n1);
            i++;
        }
    }
    
    if(fail) return -1;
    else return weight_max - arr[kk].weight;
}

int main(){
    while(scanf("%d%d", &n, &m) != EOF && (n != 0 || m != 0)){
        init();
        for(int i = 0; i < m; i++){
            scanf("%d%d%d", &arr[i].start, &arr[i].end, &arr[i].weight);
        }
        int MIN = 100000000;
        sort(arr, arr+m, cmp);
        for(int i = 0; i < m; i++){
            int tmp = func(i);
            if(tmp != -1)MIN = min(MIN, tmp);
        }
        if(MIN == 100000000){
            printf("-1
");
        }
        else{
            printf("%d
", MIN);
        }
    }
}