1416. Confidential 夜

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;
}