CF 17B Hierarchy

Nick‘s company employed n people. Now Nick needs to build a tree hierarchy of ?supervisor-surbodinate? relations in the company (this is to say that each
employee, except one, has exactly one supervisor). There are m applications written in the following form: ?employee ai is
ready to become a supervisor of employee bi at
extra cost ci?.
The qualification qj of
each employee is known, and for each application the following is true: qai?>?qbi.

Would you help Nick calculate the minimum cost of such a hierarchy, or find out that it is impossible to build it.

Input

The first input line contains integer n (1?≤?n?≤?1000)
— amount of employees in the company. The following line contains n space-separated numbers qj (0?≤?qj?≤?106)—
the employees‘ qualifications. The following line contains number m (0?≤?m?≤?10000)
— amount of received applications. The following mlines contain the applications themselves, each of them in the form of three space-separated numbers: ai,bi and ci (1?≤?ai,?bi?≤?n, 0?≤?ci?≤?106).
Different applications can be similar, i.e. they can come from one and the same employee who offered to become a supervisor of the same person but at a different cost. For each application qai?>?qbi.

Output

Output the only line — the minimum cost of building such a hierarchy, or -1 if it is impossible to build it.

Sample test(s)

input

4
7 2 3 1
4
1 2 5
2 4 1
3 4 1
1 3 5

output

11

input

3
1 2 3
2
3 1 2
3 1 3

output

-1

Note

In the first sample one of the possible ways for building a hierarchy is to take applications with indexes 1, 2 and 4, which give 11 as the minimum total cost. In the second sample it is impossible to build the required hierarchy, so the answer is -1.

预处理+贪心就可以了，因为根只有一个，所以在输入的时候预处理子节点的最小值贪心就好了=。=

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<limits.h>
using namespace std;
const int INF=0x3ffffff;
int f[1100];

int main()
{
    int n,m;
    int temp,u,v,w;
    while(cin>>n)
    {
        for(int i=1;i<=n;i++)
        {
            cin>>temp;
            f[i]=INF;
        }
        cin>>m;
        for(int i=1;i<=m;i++)
        {
            cin>>u>>v>>w;
            if(f[v]>w)//预处理最小值
                f[v]=w;
        }
        int flag=1,k=1;
        int ans=0;
        for(int i=1;i<=n;i++)//只能有一个INF，即根节点
        {
            if(f[i]==INF&&k)
            {
                ans-=INF;
                k=0;
            }
            else if(f[i]==INF)
            {
                flag=0;
                break;
            }
            ans+=f[i];
        }
        if(flag)
            cout<<ans<<endl;
        else
            cout<<-1<<endl;
    }
    return 0;
}

CF 17B Hierarchy