POJ 3522 Slim Span 最小生成树,暴力 难度:0

kruskal思想,排序后暴力枚举从任意边开始能够组成的最小生成树

#include <cstdio>
#include <algorithm>
using namespace std;

const int maxn = 101;
const int maxe = maxn * maxn / 2;
struct edge{
    int f,t,c;
    bool operator <(edge e2)const {
        return c<e2.c;
    }
}e[maxe];

int par[maxn],num[maxn],n,m;

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

int fnd(int a){
    return par[a] == a? a: par[a] = fnd(par[a]);
}

bool same(int a,int b){
    return fnd(a) == fnd(b);
}

void unit(int a,int b){
    if(!same(a,b)){
        num[fnd(a)] += num[fnd(b)];
        num[fnd(b)] = 0;
        par[fnd(b)] = fnd(a);
    }
}

int main(){
    while(scanf("%d%d",&n,&m) == 2 && n){
        for(int i = 0; i < m ; i++){
            scanf("%d%d%d",&e[i].f,&e[i].t,&e[i].c);
        }
        sort(e,e+m);
        int ans = 0x7fffffff;
        for (int i = 0;i <= m - n + 1;i++){
            init();
            int ret = 0;
            for(int j = i; num[fnd(1)] < n && j < m; j++){
                unit(e[j].f,e[j].t);
                ret = max(ret,e[j].c - e[i].c);
            }
            if(num[fnd(1)] == n)ans = min(ans,ret);
        }
        if(ans == 0x7fffffff){puts("-1");}
        else printf("%d\n",ans);
    }
    return 0;
}