POJ 1679 The Unique MST 次小生成树

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 110;
const int INF = 0x3f3f3f3f;
int map[maxn][maxn], used[maxn][maxn], lowc[maxn],pre[maxn];
int n, m, vis[maxn], Max[maxn][maxn];
void init ()//初始化
{
    for (int i=0; i<maxn; i++)
        for (int j=0; j<maxn; j++)
            if (i == j)
                map[i][j] = 0;
            else
                map[i][j] = INF;
    memset (used, 0, sizeof(used));
    memset (lowc, 0, sizeof(lowc));
    memset (pre, 0, sizeof(pre));
    memset (vis, 0, sizeof(vis));
}
/***************************/
int prim (int s)
{
    int ans = 0, mini, p;
    for (int i=1; i<=n; i++)
    {
        lowc[i] = map[s][i];
        pre[i] = s;
    }
    vis[s] = 1;
    for (int i=1; i<n; i++)
    {
        mini = INF;
        for (int j=1; j<=n; j++)
        {
            if (!vis[j] && mini>lowc[j])
            {
                mini = lowc[j];
                p = j;
            }
        }
        ans += mini;
        vis[p] = 1;
        used[p][pre[p]] = used[pre[p]][p] = 1;
        for (int j=1; j<=n; j++)
        {
            if (vis[j] && p!=j)
                Max[p][j] = Max[j][p] = max (Max[j][pre[p]], lowc[p]);//记录p于j之间最长的边
            if (!vis[j] && map[j][p]<lowc[j])
            {
                lowc[j] = map[j][p];
                pre[j] = p;
            }
        }
    }
    return ans;
}
/***************************/
int SMST (int ans)
{
    int mini = INF;
    for (int i=1; i<=n; i++)
        for (int j=i+1; j<=n; j++)
        if (!used[i][j] && map[i][j]!=INF)
        mini = min (mini, ans - Max[i][j] + map[i][j]);
    return mini;//返回最小的次小生成树的值
}
/***************************/
int main ()
{
    int t;
    scanf ("%d", &t);
    while (t --)
    {
        init ();
        scanf ("%d %d", &n, &m);
        while (m --)
        {
            int u, v, s;
            scanf ("%d %d %d", &u, &v, &s);
            map[u][v] = map[v][u] = s;
        }
        int num1 = prim(1);
        int num2 = SMST(num1);
        if (num1 != num2)
            printf ("%d\n", num1);
        else
            printf ("Not Unique!\n");
    }
    return 0;
}