hdu1598 find the most comfortable road 枚举+最小生成树

#include<cstdio>
#include<cstring>
#include<algorithm>
#define MAXN 210
#define INF 2147483646
using namespace std;

int f[MAXN], Rank[MAXN];    //Rank长度
int n, m, pos;

struct Edge{
    int u, v, val;
    //按照val从小到大排列
    friend bool operator<(const Edge&a, const Edge&b){
        return a.val < b.val;
    }
}arr[MAXN*MAXN];

void init(){
    for (int i = 0; i<MAXN; ++i)
        f[i] = i, Rank[i] = 0;
}

int find(int x){
    int i, j = x;
    while (j != f[j]) j = f[j];
    while (x != j){
        i = f[x]; f[x] = j; x = i;
    }
    return j;
}

void Union(int x, int y){
    int a = find(x), b = find(y);
    if (a == b)return;
    if (Rank[a]>Rank[b])
        f[b] = a;
    else{
        if (Rank[a] == Rank[b])
            ++Rank[b];
        f[a] = b;
    }
}

int main(){
    int u, v, speed, Q;
    while (scanf("%d%d", &n, &m) != EOF){
        for (int i = 0; i<m; ++i)
            scanf("%d%d%d", &arr[i].u, &arr[i].v, &arr[i].val);
        sort(arr, arr + m);
        scanf("%d", &Q);
        while (Q--){
            scanf("%d%d", &u, &v);
            int ans = INF;
            for (int j = 0; j < m; ++j){
                init();
                for (int k = j; k < m; ++k){
                    Union(arr[k].u, arr[k].v);
                    if (find(u) == find(v)){
                        ans = min(ans, arr[k].val - arr[j].val);    //使ans尽可能的小
                        break;
                    }
                }
            }
            if (ans == INF)
                printf("-1
");
            else 
                printf("%d
", ans);
        }
    }
    //system("pause");
    return 0;
}