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  • POJ——T2421 Constructing Roads

    http://poj.org/problem?id=2421

    Time Limit: 2000MS   Memory Limit: 65536K
    Total Submissions: 24132   Accepted: 10368

    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

     
    把已经修好的路得代价改成0,再跑最小生成树就可以了。
     1 #include <algorithm>
     2 #include <cstdio>
     3 
     4 using namespace std;
     5 
     6 const int N(1100);
     7 int n,q,u,v,w;
     8 int dis[N][N],ans;
     9 int minn,vis[N],d[N];
    10 
    11 void Prime()
    12 {
    13     for(int i=2;i<=n;i++) d[i]=dis[1][i];
    14     d[1]=vis[1]=0;
    15     for(int i=1;i<n;i++)
    16     {
    17         minn=0;
    18         for(int j=1;j<=n;j++)
    19             if(!vis[j]&&(!minn||d[j]<d[minn])) minn=j;
    20         vis[minn]=1;
    21         for(int j=1;j<=n;j++)
    22             if(!vis[j]) d[j]=min(d[j],dis[minn][j]);
    23     }
    24     for(int i=1;i<=n;i++) ans+=d[i];
    25 }
    26 
    27 int main()
    28 {
    29     scanf("%d",&n);
    30     for(int i=1;i<=n;i++)
    31       for(int j=1;j<=n;j++)
    32           scanf("%d",&dis[i][j]);
    33     scanf("%d",&q);
    34     for(;q;q--)
    35     {
    36         scanf("%d%d",&u,&v);
    37         dis[u][v]=dis[v][u]=0;
    38     }
    39     Prime();
    40     printf("%d",ans);
    41     return 0;
    42 }
    ——每当你想要放弃的时候,就想想是为了什么才一路坚持到现在。
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  • 原文地址:https://www.cnblogs.com/Shy-key/p/6818816.html
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