1416. Confidential

http://acm.timus.ru/problem.aspx?space=1&num=1416

最小生成树 和次小生成树

代码：

#include<iostream>

#include<stdio.h>

#include<string.h>

#include<math.h>

#include<algorithm>

#include<vector>

#include<set>

#include<map>

#include<string>

#include<queue>

#include<stack>

#include <iomanip>

using namespace std;

#define LL long long

const int INF=0x3f3f3f3f;

//priority_queue<int,vector<int>,greater<int> >qt;

const int N=505;

int f[N];

int a[N][N];

vector<int>tree[N];

vector<int>value[N];

struct node

{

    int l,r;

    int k;

    bool used;

}side[N*N];

bool cmp(node x,node y)

{

    return x.k<y.k;

}

int findx(int x)

{

    if(f[x]!=x)

    f[x]=findx(f[x]);

    return f[x];

}

int Kruskal(int n,int m)

{

    sort(side,side+m,cmp);

    for(int i=1;i<=n;++i)

    {tree[i].clear();value[i].clear();}

    for(int i=1;i<=n;++i)

    f[i]=i;

    int sum=0;

    for(int i=0;i<m;++i)

    {

        int l=side[i].l;

        int r=side[i].r;

        if(findx(l)!=findx(r))

        {

            side[i].used=true;

            sum+=side[i].k;

            f[findx(l)]=findx(r);

            tree[l].push_back(r);

            tree[r].push_back(l);

            value[l].push_back(side[i].k);

            value[r].push_back(side[i].k);

        }

    }

    return sum;

}

void dfs(int s,int x,int pre,int k)

{

    a[s][x]=k;

    for(unsigned int i=0;i<tree[x].size();++i)

    {

        if(tree[x][i]==pre)

        continue;

        dfs(s,tree[x][i],x,max(k,value[x][i]));

    }

}

int Ctree(int n,int m,int MIN)

{

    for(int i=1;i<=n;++i)

    dfs(i,i,-1,0);

    int sum=-1;

    for(int i=0;i<m;++i)

    {

        int l=side[i].l;

        int r=side[i].r;

        if(side[i].used==false)

        {

            if(sum==-1) sum=MIN-a[l][r]+side[i].k;

            else sum=min(sum,MIN-a[l][r]+side[i].k);

        }

    }

    return sum;

}

int main()

{

    //freopen("data.in","r",stdin);

    int n,m;

    while(cin>>n>>m)

    {

        for(int i=0;i<m;++i)

        {

            cin>>side[i].l>>side[i].r>>side[i].k;

            side[i].used=false;

        }

        int MIN=Kruskal(n,m);

        int CMIN=Ctree(n,m,MIN);

        cout<<"Cost: "<<MIN<<endl;

        cout<<"Cost: "<<CMIN<<endl;

    }

    return 0;

}