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  • HDU 1102 Constructing Roads

    Constructing Roads

    Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
    Total Submission(s): 14935    Accepted Submission(s): 5691

    Problem Description
    There are N villages, which are numbered from 1 to N, and you should build some roads such that every two villages can connect to each other. We say two village A and B are connected, if and only if there is a road between A and B, or there exists a village C such that there is a road between A and C, and C and B are connected. 

    We know that there are already some roads between some villages and your job is the build some roads such that all the villages are connect and the length of all the roads built is minimum.
     
    Input
    The first line is an integer N (3 <= N <= 100), which is the number of villages. Then come N lines, the i-th of which contains N integers, and the j-th of these N integers is the distance (the distance should be an integer within [1, 1000]) between village i and village j.

    Then there is an integer Q (0 <= Q <= N * (N + 1) / 2). Then come Q lines, each line contains two integers a and b (1 <= a < b <= N), which means the road between village a and village b has been built.
     
    Output
    You should output a line contains an integer, which is the length of all the roads to be built such that all the villages are connected, and this value is minimum. 
     
    Sample Input
    3
    0 990 692
    990 0 179
    692 179 0
    1
    1 2
     
    Sample Output
    179
     
    Source
     
     
    Source Code:
    #include <iostream>
    #include <algorithm>
    
    using namespace std;
    
    struct road{
        int start;
        int end;
        int cost;
    };
    
    int maze[110][110];
    road RoadsArr[100000];
    int Root[110];
    
    bool cmp(road a,road b){
        return a.cost<=b.cost;
    }
    
    void initRoot(int length){
        for(int i=1;i<=length;++i)
            Root[i]=-1;
    }
    
    int findRoot(int x){
        if(Root[x]==-1)
            return x;
        else{
            int tmp=findRoot(Root[x]);
            Root[x]=tmp;
            return tmp;
        }
    }
    
    int Kruskal(int length){
        int answer=0;
        for(int i=0;i<length;++i){
            int Root_a=findRoot(RoadsArr[i].start);
            int Root_b=findRoot(RoadsArr[i].end);
            if(Root_a!=Root_b){
                Root[Root_a]=Root_b;
                answer+=RoadsArr[i].cost;
            }
        }
        return answer;
    }
    
    int main(){
        int N,Q;
        while(cin>>N){
            initRoot(N);
            int index=0;
            for(int i=1;i<=N;++i){
                for(int j=1;j<=N;++j){
                    cin>>maze[i][j];
                    if(i!=j){
                        RoadsArr[index].start=i;
                        RoadsArr[index].end=j;
                        RoadsArr[index].cost=maze[i][j];
                        ++index;
                    }
                }
            }
            sort(RoadsArr,RoadsArr+index,cmp);
            cin>>Q;
            int city_a,city_b;
            for(int i=0;i<Q;++i){
                cin>>city_a>>city_b;
                int Root_a=findRoot(city_a);
                int Root_b=findRoot(city_b);
                if(Root_a!=Root_b)
                    Root[Root_a]=Root_b;
            }
            int answer=Kruskal(index);
            cout<<answer<<endl;
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/Murcielago/p/4243527.html
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