POJ1679判断最小生成树是否唯一

判断最小生成树是否唯一的思路：
  (1) 对图中每条边，扫描其它边，如果存在权值相同的边，则对该边作标记
  (2) 然后用Kruskal算法求MST
  (3) 求得MST后，如果该MST中为包含作了标记的边，即可判定MST唯一;
       如果包含作了标记的边，则依次去掉这些边再求MST,如果求得的MST
       权值与原MST的权值相同，即可判定MST不唯一

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
using namespace std;
#define N 105
#define M 10050
struct Edge
{
    int u,v,w;
    int equal;
    int del;
    int used;
}edge[M];
int father[N],rank[N];
int n,m;
bool first;

bool cmp(Edge a,Edge b)
{
    return a.w < b.w ;
}

void Init()
{
    for(int i=1; i<=n; i++)
    {
        rank[i] = 1;
        father[i] = i;
    }
}

int find(int x)
{
    if(father[x] != x)
    father[x] = find(father[x]);
    return father[x];
}

void merge(int x,int y)
{
    int xf = find(x);
    int yf = find(y);
    if(rank[xf] > rank[yf])
    {
        rank[xf] += rank[yf];
        father[yf] = xf;
    }
    else
    {
        rank[yf] += rank[xf];
        father[xf] = yf;
    }
}

int Kruskal()
{
    int num = 0;
    int sum = 0;
    Init();
    for(int i=0; i<m; i++)
    {
        int u = edge[i].u ;
        int v = edge[i].v ;
        if(edge[i].del) continue;
        if(find(u) != find(v))
        {
            num++;
            sum += edge[i].w;
            merge(u,v);
            if(first) edge[i].used = 1;
        }
        if(num==n-1) break;
    }
    if(num<n-1) return -1;
    return sum;
}

int main()
{
    int T;
    int u,v,w;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&m);
        for(int i=0; i<m; i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            edge[i].u = u ; edge[i].v = v ; edge[i].w = w ;
            edge[i].equal = 0 ; edge[i].del = 0 ; edge[i].used = 0 ;
        }
        for(int i=0; i<m; i++)
        for(int j=i+1; j<m; j++)
        {
            if(edge[i].w == edge[j].w)
            edge[i].equal = edge[j].equal = 1;
        }
        sort(edge,edge+m,cmp);
        first = 1;
        int sum1 = Kruskal();
        int flag = 1;
        first = 0;
        for(int i=0; i<m; i++)
        {
            if(edge[i].used && edge[i].equal)
            {
                edge[i].del = 1;
                int sum2 = Kruskal();
                if(sum1 == sum2)
                {
                    printf("Not Unique!
");
                    flag = 0;
                    break;
                }
                edge[i].del = 0;
            }
        }
        if(flag) printf("%d
",sum1);
    }
    return 0;
}