poj2377 - Bad Cowtractors

                               想看更多的解题报告:http://blog.csdn.net/wangjian8006/article/details/7870410
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题目大意：谷仓之间有一些路径长度，然后要在这些谷仓之间建立一些互联网，花费的成本与长度成正比，，并且要使这些边连起来看的像一课“树”，然后使成本最大
解题思路：最大生成树
用kruskal在最小生成树的基础上，将排序从大到小排序，这样就是一个最大生成树了

/*
Memory 472K
Time 63MS
*/

#include <iostream>
#include <algorithm>
using namespace std;
#define MAXV 1001
#define MAXM 20010

class CEdge{
public:
	int m_start,m_end,m_value;
};

class CMaxSpanTree{
private:
	CEdge *m_edge;					//结构体保存边的信息
	int *m_nParentSet;			//保存并查集的父亲数组

	int m_nVerCount;			//点的个数
	int m_nEdgeCount;			//边的个数
	bool m_bFlag;				//判断是否是连通图

	int m_nAns;					//最大生成树的边和

	bool Union(int x,int y);		//并查集的合并函数
	int find(int x);				//并查集寻找根节点函数
public:
	CMaxSpanTree(int VerCount);
	~CMaxSpanTree();
	void AddEdge(int s,int t,int w);			//增加一条边
	void Run();									//运行，kruskal算法计算最大生成树
	int GetAns();								//得到答案
};

bool cmp(CEdge a,CEdge b){				//这边用kruskal算法时使排序按照边值从大到小排序
	return a.m_value>b.m_value;
}

CMaxSpanTree::CMaxSpanTree(int nVerCount){
	m_edge = new CEdge[MAXM];
	m_nParentSet = new int[MAXV];

	m_nEdgeCount = 0;
	m_nVerCount = nVerCount;

	m_nAns = 0;
	m_bFlag = false;				//初始设为不连通
	
	for(int i = 0;i <= nVerCount;i++){			//并查集父亲数组初值
		m_nParentSet[i] = i;
	}
}
CMaxSpanTree::~CMaxSpanTree(){
	delete []m_edge;
	delete []m_nParentSet;
}

void CMaxSpanTree::AddEdge(int s,int t,int w){
	m_edge[m_nEdgeCount].m_start = s;
	m_edge[m_nEdgeCount].m_end = t;
	m_edge[m_nEdgeCount].m_value = w;
	m_nEdgeCount++;
}

int CMaxSpanTree::find(int x){
	if(x == m_nParentSet[x])
		return x;
	int rt = find(m_nParentSet[x]);
	m_nParentSet[x] = rt;
	return rt;
}

bool CMaxSpanTree::Union(int x,int y){
	int fx = find(x);
	int fy = find(y);

	if (fx == fy){
		return 0;
	}
	m_nParentSet[fx] = fy;
	return 1;
}

void CMaxSpanTree::Run(){
	sort(m_edge,m_edge+m_nEdgeCount,cmp);

	int nCnt = 0 ,i;

	for(i = 0;i < m_nEdgeCount;i++){
		if(Union(m_edge[i].m_start,m_edge[i].m_end)){
			m_nAns += m_edge[i].m_value;
			nCnt++;
			if(nCnt == m_nVerCount - 1){
				m_bFlag = true;
				return;
			}
		}
	}
}

int CMaxSpanTree::GetAns(){
	return m_bFlag?m_nAns:-1;
}

int main(){
	int n,m;
	int a,b,c;
	while(~scanf("%d%d",&n,&m)){
		CMaxSpanTree tree(n);
		while(m--){
			scanf("%d%d%d",&a,&b,&c);
			tree.AddEdge(a,b,c);
		}

		tree.Run();

		cout<<tree.GetAns()<<endl;
	}
	return 0;
}