poj1258 Agri-Net(Prime || Kruskal)
阿新 • • 發佈:2017-12-04
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題目鏈接
http://poj.org/problem?id=1258
題意
有n個農場,現在要在n個農場之間鋪設光纖使得n個農場連接起來,求鋪設光纖的最短距離。
思路
最小生成樹問題,使用Prime算法或者Kruskal算法解決。
代碼
Prime算法:
1 #include <algorithm> 2 #include <iostream> 3 #include <cstring> 4 #include <cstdio> 5 using namespace std; 6 7 const int INF = 0x7fffffff; 8 const int N = 100 + 10; 9 int map[N][N]; 10 int dist[N]; 11 int n; 12 13 void prime() 14 { 15 int min_edge, min_node; 16 for (int i = 0; i < n; i++) 17 dist[i] = INF; 18 int ans = 0; 19 int now = 0; 20 for (int i = 0; i < n - 1; i++) 21 { 22 dist[now] = -1; 23 min_edge = INF; 24 for (int j = 0; j < n; j++) 25 { 26 if (j != now && dist[j] >= 0) 27 { 28 if (map[now][j]>0) 29 dist[j] = min(dist[j], map[now][j]); 30 if (dist[j] < min_edge)31 { 32 min_edge = dist[j]; //min_edge存儲與當前結點相連的最短的邊 33 min_node = j; 34 } 35 } 36 } 37 ans += min_edge; 38 now = min_node; 39 } 40 printf("%d\n", ans); 41 } 42 43 int main() 44 { 45 //freopen("poj1258.txt", "r", stdin); 46 while (scanf("%d", &n) == 1) 47 { 48 memset(map, 0, sizeof(map)); //註意初始化 49 for (int i = 0; i < n; i++) 50 for (int j = 0; j < n; j++) 51 cin >> map[i][j]; 52 prime(); 53 } 54 return 0; 55 }
Kruskal算法:
1 #include <algorithm> 2 #include <iostream> 3 #include <cstring> 4 #include <cstdio> 5 #include <vector> 6 using namespace std; 7 8 struct Edge 9 { 10 int a, b, dist; 11 12 Edge() {} 13 Edge(int a, int b, int d) :a(a), b(b), dist(d) {} 14 }; 15 16 bool cmp(Edge e1, Edge e2) 17 { 18 return e1.dist < e2.dist; 19 } 20 21 const int N = 100 + 10; 22 vector<Edge> v; 23 int p[N]; 24 int map[N][N]; 25 int n; 26 27 int find_root(int x) 28 { 29 if (p[x] == -1) 30 return x; 31 else return find_root(p[x]); 32 } 33 34 void kruskal() 35 { 36 memset(p, -1, sizeof(p)); 37 sort(v.begin(), v.end(), cmp); //將邊按邊長從短到長排序 38 int ans = 0; 39 for (int i = 0; i < v.size(); i++) 40 { 41 int ra = find_root(v[i].a); 42 int rb = find_root(v[i].b); 43 if (ra != rb) 44 { 45 ans += v[i].dist; 46 p[ra] = rb; 47 } 48 } 49 printf("%d\n", ans); 50 } 51 52 int main() 53 { 54 //freopen("poj1258.txt", "r", stdin); 55 while (scanf("%d", &n) == 1) 56 { 57 v.clear(); //註意初始化 58 for (int i = 0; i < n; i++) 59 for (int j = 0; j < n; j++) 60 cin >> map[i][j]; 61 for (int i = 0; i < n; i++) 62 for (int j = 0; j < n; j++) 63 if (i < j) v.push_back(Edge(i, j, map[i][j])); 64 kruskal(); 65 } 66 return 0; 67 }
poj1258 Agri-Net(Prime || Kruskal)