POJ 1679 The Unique MST

Description
Given a connected undirected graph, tell if its minimum spanning tree is unique.
Definition 1 (Spanning Tree): Consider a connected, undirected graph G = (V, E). A spanning tree of G is a subgraph of G, say T = (V’, E’), with the following properties:
1. V’ = V.
2. T is connected and acyclic.
Definition 2 (Minimum Spanning Tree): Consider an edge-weighted, connected, undirected graph G = (V, E). The minimum spanning tree T = (V, E’) of G is the spanning tree that has the smallest total cost. The total cost of T means the sum of the weights on all the edges in E’.

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【题目分析】
关于最小生成树是否唯一的问题。只需要计算一下删除任意一条原有的生成树的边，然后再跑一边最小生成树，然后比较一下是否相等就可以了。

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【代码】

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;struct edge{    int a,b,w;}c[20000];int f[110],list[110];inline int gf(int k){    if (f[k]==k) return k;    else return f[k]=gf(f[k]);}inline bool cmp(edge a,edge b){return a.w<b.w;}inline void un(int a,int b){    int fa=gf(a),fb=gf(b);    if (fa==fb) return;    else f[fa]=fb;    return;}inline void kru(){    int n,m,ans=0,ans2=0,k2,k=0;    scanf("%d%d",&n,&m);    memset(c,0,sizeof c);    memset(list,0,sizeof list);    for (int i=1;i<=m;++i) scanf("%d%d%d",&c[i].a,&c[i].b,&c[i].w);    for (int i=1;i<=n;++i) f[i]=i;    sort(c+1,c+m+1,cmp);    for (int i=1;i<=m&&k<n-1;++i)    {        int f1=gf(c[i].a),f2=gf(c[i].b);        if (f1!=f2)        {            un(f1,f2);            ++k;            ans+=c[i].w;            list[k]=i;        }    }    for (int i=1;i<n;++i)    {        ans2=0,k2=0;        for (int j=1;j<=n;++j) f[j]=j;        for (int j=1;j<=m;++j)        {            if (j==list[i]) continue;            int f1=gf(c[j].a),f2=gf(c[j].b);            if (f1!=f2)            {                un(f1,f2);                k2++;                ans2+=c[j].w;            }        }        if (k2!=n-1) continue;        if (ans==ans2){            printf("Not Unique!\n");            return ;        }    }    printf("%d\n",ans);}int main(){    int tt;    scanf("%d",&tt);    for (int z=1;z<=tt;++z)    {        kru();    }}