hdu 1102 Constructing Roads(最小生成树 Prim)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1102

3
0 990 692
990 0 179
692 179 0
1
1 2

179

代码例如以下：

#include <cstdio>
#include <cstring>
#define INF 0x3f3f3f3f
#define MAXN 517
//创建m二维数组储存图表，low数组记录每2个点间最小权值，visited数组标记某点是否已訪问
int m[MAXN][MAXN], low[MAXN], visited[MAXN];
int n;
int prim( )
{
    int i, j;
    int pos, minn, result=0;
    // memset(visited,0,sizeof(visited));
    for(i = 1; i <= n; i++)
        visited[i] = 0;
    visited[1] = 1;
    pos = 1;          //从某点開始，分别标记和记录该点
    for(i = 1; i <= n; i++)     //第一次给low数组赋值
    {
        if(i != pos)
            low[i] = m[pos][i];
        else
            low[i] = 0;
    }
    for(i = 1; i <= n; i++) //再执行n-1次
    {
        minn = INF;   //找出最小权值并记录位置
        pos = -1;
        for(j = 1; j <= n; j++)
        {
            if(visited[j]==0 && minn>low[j])
            {
                minn = low[j];
                pos = j;
            }
        }
        if(pos == -1)
            continue;
        result += minn;   //最小权值累加
        visited[pos] = 1;   //标记该点
        for(j = 1; j <= n; j++)   //更新权值
            if(!visited[j] && low[j]>m[pos][j])
                low[j] = m[pos][j];
    }
    return result;
}
int main()
{
    int tt;
    while(~scanf("%d",&n))
    {
        memset(m,INF,sizeof(m));   //全部权值初始化为最大
        for(int i = 1; i <= n; i++)
        {
            for(int j = 1; j <= n; j++)
            {
                scanf("%d",&tt);
                if(tt < m[j][i])
                    m[i][j] = m[j][i] = tt;
            }
        }
        int Q, a, b;
        scanf("%d",&Q);
        for(int i = 0; i < Q; i++)
        {
            scanf("%d%d",&a,&b);
            m[a][b] = m[b][a] = 0;
        }
        int ans = prim( );
        printf("%d\n",ans);
    }
    return 0;
}