The Unique MST POJ

这是一个次小生成树的基础题，这个题的想法，就是先写一个最小生成树，建立最小生成树的时候，把每个点的边还有结点用vector保存无向图，然后遍历每一个结点，找出这条边上的最大值，如果这个点没有遍历过那就更新最大值。

#include <iostream>#include <algorithm>#include <queue>#include <cstring>#include <cstdio>using namespace std;const int INF = 0x7fffffff;const int MAX = 10001;int n,m;int num;int p[MAX];int max1[101][101];int dist[105][105];vector<int> g[MAX];struct Edge{    int from;    int to;    int w;    bool flag;} e[MAX];struct Node{    int seq;    int max;};bool cmp(const Edge &a, const Edge &b){    return a.w < b.w;}void makeSet(){    for(int i = 0; i <= n; i++)    {        p[i] = i;    }}int findSet(int x){    if(x != p[x])        p[x] = findSet(p[x]);    return p[x];}void addEdge(int from, int to, int w){    g[from].push_back(to);    g[to].push_back(from);    dist[from][to] = w;    dist[to][from] = w;}int kruscal(){    int i,j;    int x, y;    int edgeNum = 0;    int result = 0;    makeSet();    std::sort(e,e+m,cmp);    for(i = 0; i < m; i++)    {        x = findSet(e[i].from);        y = findSet(e[i].to);        if(x != y)        {            edgeNum++;            addEdge(e[i].from,e[i].to,e[i].w);            addEdge(e[i].to,e[i].from,e[i].w);            e[i].flag = true;            p[x] = y;            result += e[i].w;        }    }    return edgeNum == n-1 ? result : -1;}void bfs(int p){    int i,j;    bool used[101];    memset(used,0,sizeof(used));    std::queue<Node> que;    Node now,adj;    now.max = 0;    now.seq = p;    que.push(now);    used[p] = true;    while(!que.empty())    {        Node q = que.front();        que.pop();        for(i = 0; i < g[q.seq].size(); i++)        {            adj.seq = g[q.seq][i];            adj.max = dist[q.seq][adj.seq];            if(!used[adj.seq])            {                if(q.max > adj.max)                    adj.max = q.max;                max1[p][adj.seq] = adj.max;                used[adj.seq] = true;                que.push(adj);            }        }    }}void second_MST(){    int i,j;    int mst = kruscal();    for(i = 1; i <= n; i++)        bfs(i);    int smst = INF;    for(i = 0; i < m; i++)    {        if(!e[i].flag)        {            if(mst + e[i].w - max1[e[i].from][e[i].to] < smst)                smst = mst + e[i].w - max1[e[i].from][e[i].to];        }    }    if(smst == mst)        printf("Not Unique!\n");    else        printf("%d\n",mst);}int main(){    int i,j;    int cases;    int a,b,w;    scanf("%d",&cases);    while(cases--)    {        memset(dist,0,sizeof(dist));        scanf("%d %d",&n,&m);        for(i = 0; i < m; i++)        {            scanf("%d %d %d",&e[i].from,&e[i].to,&e[i].w);            e[i].flag = false;        }        num = 0;        second_MST();    }    return 0;}