The Unique MST 1679（最小生成树的不唯一性）

The Unique MST

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 24076		Accepted: 8551

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'.

Input
The first line contains a single integer t (1 <= t <= 20), the number of test cases. Each case represents a graph. It begins with a line containing two integers n and m (1 <= n <= 100), the number of nodes and edges. Each of the
following m lines contains a triple (xi, yi, wi), indicating that xi and yi are connected by an edge with weight = wi. For any two nodes, there is at most one edge connecting them.
Output
For each input, if the MST is unique, print the total cost of it, or otherwise print the string 'Not Unique!'.
Sample Input

2
3 3
1 2 1
2 3 2
3 1 3
4 4
1 2 2
2 3 2
3 4 2
4 1 2

Sample Output

3
Not Unique!

#include<stdio.h>
#include<string.h>
#define mx 0xfffffff
int g[110][110],v[110],dis[110];
int n,m;
void prim()
{
int i,j,k,flag,min,sum=0;
memset(v,0,sizeof(v));
for(i=1;i<=n;i++)
dis[i]=g[1][i];
dis[1]=0;
v[1]=1;
for(j=1;j<n;j++)
{
min=mx;k=1;flag=0;
for(i=1;i<=n;i++)
{
if(!v[i]&&dis[i]<min)
{
min=dis[i];
k=i;
}
}
for(i=1;i<=n;i++)
{
if(v[i]&&g[k][i]==min)
{
flag++;
}
}
if(flag>1)
{
printf("Not Unique!\n");
return ;
}
sum+=min;
v[k]=1;
for(i=1;i<=n;i++)
{
if(!v[i]&&dis[i]>g[k][i])
dis[i]=g[k][i];
}
}
printf("%d\n",sum);
}
int main(){
int t;
scanf("%d",&t);
while(t--)
{
int i,j;
scanf("%d%d",&n,&m);
for(i=0;i<=n;i++)
{
for(j=0;j<=n;j++)
{
if(i==j)
g[i][j]=0;
else
g[i][j]=mx;
}
}
while(m--)
{
int a,b,c;
scanf("%d%d%d",&a,&b,&c);
if(g[a][b]>c)
g[a][b]=g[b][a]=c;
}
prim();
}
return 0;
}