hdoj1233 还是畅通工程（Prime || Kruskal）

题目链接

http://acm.hdu.edu.cn/showproblem.php?pid=1233

思路

最小生成树问题，使用Prime算法或者Kruskal算法解决。

代码

Prime算法：

#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;

const int INF = 0xfffffff;
const int N = 100 + 10;
int map[N][N];
int dist[N];    //存储从起点到其余各点的距离，不断更新
int n;

void prime()
{
    int min_edge, min_node;
    for (int i = 1;i <= n;i++)
        dist[i] = INF;
    int ans = 0;
    int now = 1;
    for (int i = 1;i < n;i++)
    {
        dist[now] = -1;
        min_edge = INF;
        for (int j = 1;j <= n;j++)
        {
            if (j != now && dist[j] >= 0)
            {
                if (map[now][j]>0)
                    dist[j] = min(dist[j], map[now][j]);
                if (dist[j] < min_edge)
                {
                    min_edge = dist[j];    //min_edge存储与当前结点相连的最短的边
                    min_node = j;
                }
            }
        }
        ans += min_edge;    //ans存储最小生成树的长度
        now = min_node;
    }
    printf("%d
", ans);
}

int main()
{
    //freopen("hdoj1233.txt", "r", stdin);
    while (scanf("%d", &n) == 1 && n)
    {
        memset(map, 0, sizeof(map));
        int a, b, c;
        int nums = n*(n - 1) / 2;
        for (int i = 0; i < nums; i++)
        {
            scanf("%d%d%d", &a, &b, &c);
            map[a][b] = c;
            map[b][a] = c;
        }
        prime();
    }
    return 0;
}

Kruskal算法：

#include <algorithm>
#include <cstring>
#include <cstdio>
#include <vector>
using namespace std;

struct Edge
{
    int a, b, dist;

    Edge() {}
    Edge(int a, int b, int d) :a(a), b(b), dist(d) {}
    bool operator < (Edge edge)    //按边长从短到长排序
    {
        return dist < edge.dist;
    }
};

const int N = 100 + 10;
int p[N];    //并查集使用
vector<Edge> v;
int n;

int find_root(int x)
{
    if (p[x] == -1)
        return x;
    else return find_root(p[x]);
}

void kruskal()
{
    memset(p, -1, sizeof(p));
    sort(v.begin(), v.end());
    int ans = 0;
    for (int i = 0; i < v.size(); i++)
    {
        int ra = find_root(v[i].a);
        int rb = find_root(v[i].b);
        if (ra != rb)
        {
            ans += v[i].dist;
            p[ra] = rb;
        }
    }
    printf("%d
", ans);
}

int main()
{
    //freopen("hdoj1233.txt", "r", stdin);
    while (scanf("%d", &n) == 1 && n)
    {
        int a, b, d;
        int nums = n*(n - 1) / 2;
        v.clear();
        for (int i = 0; i < nums; i++)
        {
            scanf("%d%d%d", &a, &b, &d);
            v.push_back(Edge(a, b, d));
        }
        kruskal();
    }
}