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Arborele minim de acoperire a produsului

Având în vedere un graf conex și nedirecționat, un arbore de întindere al acelui graf este un subgraf care este un arbore și conectează toate vârfurile împreună. Un singur grafic poate avea mai mulți arbori de acoperire diferiți. Un arbore de întindere a produsului minim pentru un grafic ponderat conectat și nedirecționat este un arbore de întindere cu un produs de greutate mai mic sau egal cu produsul de greutate al oricărui alt arbore de întindere. Produsul ponderal al unui arbore spanning este produsul greutăților corespunzătoare fiecărei margini a arborelui spanning. Toate ponderile graficului dat vor fi pozitive pentru simplitate.

Exemple:

cum să găsiți dimensiunea monitorului

Arborele minim de acoperire a produsului



Minimum Product that we can obtain is 180 for above graph by choosing edges 0-1 1-2 0-3 and 1-4

Această problemă poate fi rezolvată folosind algoritmi standard de arbore de acoperire minim, cum ar fi Kruskal ( https://www.geeksforgeeks.org/dsa/kruskals-minimum-spanning-tree-algorithm-greedy-algo-2/ )şi prim algoritmul lui, dar trebuie să ne modificăm graficul pentru a folosi acești algoritmi. Algoritmii arborelui de acoperire minimă încearcă să minimizeze suma totală a greutăților aici trebuie să minimizăm produsul total al greutăților. Putem folosi proprietatea lui logaritmi pentru a depăși această problemă. 
După cum știm 

 log(w1* w2 * w3 * …. * wN) = log(w1) + log(w2) + log(w3) ….. + log(wN)


Putem înlocui fiecare greutate a graficului cu valoarea sa log, apoi aplicăm orice algoritm de arbore de întindere minim care va încerca să minimizeze suma log(wi) care, la rândul său, minimizează produsul de greutate. 
De exemplu grafic pașii sunt prezentați mai jos diagramă 
 

Arborele minim de acoperire a produsului

powershell mai mic sau egal cu


În codul de mai jos, am construit mai întâi graficul log din graficul de intrare dat, apoi acel grafic este dat ca intrare la algoritmul MST al lui prim, care va minimiza suma totală a greutăților arborelui. Deoarece ponderile graficului modificat sunt logaritmi ai graficului de intrare real, minimizăm de fapt produsul greutăților arborelui de întindere.  

C++
// A C++ program for getting minimum product // spanning tree The program is for adjacency matrix // representation of the graph #include    // Number of vertices in the graph #define V 5 // A utility function to find the vertex with minimum // key value from the set of vertices not yet included // in MST int minKey(int key[] bool mstSet[]) {  // Initialize min value  int min = INT_MAX min_index;  for (int v = 0; v < V; v++)  if (mstSet[v] == false && key[v] < min)  min = key[v] min_index = v;  return min_index; } // A utility function to print the constructed MST // stored in parent[] and print Minimum Obtainable // product int printMST(int parent[] int n int graph[V][V]) {  printf('Edge Weightn');  int minProduct = 1;  for (int i = 1; i < V; i++) {  printf('%d - %d %d n'  parent[i] i graph[i][parent[i]]);  minProduct *= graph[i][parent[i]];  }  printf('Minimum Obtainable product is %dn'  minProduct); } // Function to construct and print MST for a graph // represented using adjacency matrix representation // inputGraph is sent for printing actual edges and // logGraph is sent for actual MST operations void primMST(int inputGraph[V][V] double logGraph[V][V]) {  int parent[V]; // Array to store constructed MST  int key[V]; // Key values used to pick minimum  // weight edge in cut  bool mstSet[V]; // To represent set of vertices not  // yet included in MST  // Initialize all keys as INFINITE  for (int i = 0; i < V; i++)  key[i] = INT_MAX mstSet[i] = false;  // Always include first 1st vertex in MST.  key[0] = 0; // Make key 0 so that this vertex is  // picked as first vertex  parent[0] = -1; // First node is always root of MST  // The MST will have V vertices  for (int count = 0; count < V - 1; count++) {  // Pick the minimum key vertex from the set of  // vertices not yet included in MST  int u = minKey(key mstSet);  // Add the picked vertex to the MST Set  mstSet[u] = true;  // Update key value and parent index of the  // adjacent vertices of the picked vertex.  // Consider only those vertices which are not yet  // included in MST  for (int v = 0; v < V; v++)  // logGraph[u][v] is non zero only for  // adjacent vertices of m mstSet[v] is false  // for vertices not yet included in MST  // Update the key only if logGraph[u][v] is  // smaller than key[v]  if (logGraph[u][v] > 0 && mstSet[v] == false && logGraph[u][v] < key[v])  parent[v] = u key[v] = logGraph[u][v];  }  // print the constructed MST  printMST(parent V inputGraph); } // Method to get minimum product spanning tree void minimumProductMST(int graph[V][V]) {  double logGraph[V][V];  // Constructing logGraph from original graph  for (int i = 0; i < V; i++) {  for (int j = 0; j < V; j++) {  if (graph[i][j] > 0)  logGraph[i][j] = log(graph[i][j]);  else  logGraph[i][j] = 0;  }  }  // Applying standard Prim's MST algorithm on  // Log graph.  primMST(graph logGraph); } // driver program to test above function int main() {  /* Let us create the following graph  2 3  (0)--(1)--(2)  | /  |  6| 8/ 5 |7  | /  |  (3)-------(4)  9 */  int graph[V][V] = {  { 0 2 0 6 0 }  { 2 0 3 8 5 }  { 0 3 0 0 7 }  { 6 8 0 0 9 }  { 0 5 7 9 0 }  };  // Print the solution  minimumProductMST(graph);  return 0; } 
Java
// A Java program for getting minimum product // spanning tree The program is for adjacency matrix // representation of the graph import java.util.*; class GFG {  // Number of vertices in the graph  static int V = 5;  // A utility function to find the vertex with minimum  // key value from the set of vertices not yet included  // in MST  static int minKey(int key[] boolean[] mstSet)  {  // Initialize min value  int min = Integer.MAX_VALUE min_index = 0;  for (int v = 0; v < V; v++) {  if (mstSet[v] == false && key[v] < min) {  min = key[v];  min_index = v;  }  }  return min_index;  }  // A utility function to print the constructed MST  // stored in parent[] and print Minimum Obtainable  // product  static void printMST(int parent[] int n int graph[][])  {  System.out.printf('Edge Weightn');  int minProduct = 1;  for (int i = 1; i < V; i++) {  System.out.printf('%d - %d %d n'  parent[i] i graph[i][parent[i]]);  minProduct *= graph[i][parent[i]];  }  System.out.printf('Minimum Obtainable product is %dn'  minProduct);  }  // Function to construct and print MST for a graph  // represented using adjacency matrix representation  // inputGraph is sent for printing actual edges and  // logGraph is sent for actual MST operations  static void primMST(int inputGraph[][] double logGraph[][])  {  int[] parent = new int[V]; // Array to store constructed MST  int[] key = new int[V]; // Key values used to pick minimum  // weight edge in cut  boolean[] mstSet = new boolean[V]; // To represent set of vertices not  // yet included in MST  // Initialize all keys as INFINITE  for (int i = 0; i < V; i++) {  key[i] = Integer.MAX_VALUE;  mstSet[i] = false;  }  // Always include first 1st vertex in MST.  key[0] = 0; // Make key 0 so that this vertex is  // picked as first vertex  parent[0] = -1; // First node is always root of MST  // The MST will have V vertices  for (int count = 0; count < V - 1; count++) {  // Pick the minimum key vertex from the set of  // vertices not yet included in MST  int u = minKey(key mstSet);  // Add the picked vertex to the MST Set  mstSet[u] = true;  // Update key value and parent index of the  // adjacent vertices of the picked vertex.  // Consider only those vertices which are not yet  // included in MST  for (int v = 0; v < V; v++) // logGraph[u][v] is non zero only for  // adjacent vertices of m mstSet[v] is false  // for vertices not yet included in MST  // Update the key only if logGraph[u][v] is  // smaller than key[v]  {  if (logGraph[u][v] > 0  && mstSet[v] == false  && logGraph[u][v] < key[v]) {  parent[v] = u;  key[v] = (int)logGraph[u][v];  }  }  }  // print the constructed MST  printMST(parent V inputGraph);  }  // Method to get minimum product spanning tree  static void minimumProductMST(int graph[][])  {  double[][] logGraph = new double[V][V];  // Constructing logGraph from original graph  for (int i = 0; i < V; i++) {  for (int j = 0; j < V; j++) {  if (graph[i][j] > 0) {  logGraph[i][j] = Math.log(graph[i][j]);  }  else {  logGraph[i][j] = 0;  }  }  }  // Applying standard Prim's MST algorithm on  // Log graph.  primMST(graph logGraph);  }  // Driver code  public static void main(String[] args)  {  /* Let us create the following graph  2 3  (0)--(1)--(2)  | /  |  6| 8/ 5 |7  | /  |  (3)-------(4)  9 */  int graph[][] = {  { 0 2 0 6 0 }  { 2 0 3 8 5 }  { 0 3 0 0 7 }  { 6 8 0 0 9 }  { 0 5 7 9 0 }  };  // Print the solution  minimumProductMST(graph);  } } // This code has been contributed by 29AjayKumar 
Python3
# A Python3 program for getting minimum # product spanning tree The program is  # for adjacency matrix representation # of the graph  import math # Number of vertices in the graph  V = 5 # A utility function to find the vertex # with minimum key value from the set  # of vertices not yet included in MST  def minKey(key mstSet): # Initialize min value  min = 10000000 min_index = 0 for v in range(V): if (mstSet[v] == False and key[v] < min): min = key[v] min_index = v return min_index # A utility function to print the constructed  # MST stored in parent[] and print Minimum  # Obtainable product  def printMST(parent n graph): print('Edge Weight') minProduct = 1 for i in range(1 V): print('{} - {} {} '.format(parent[i] i graph[i][parent[i]])) minProduct *= graph[i][parent[i]] print('Minimum Obtainable product is {}'.format( minProduct)) # Function to construct and print MST for  # a graph represented using adjacency  # matrix representation inputGraph is # sent for printing actual edges and  # logGraph is sent for actual MST  # operations  def primMST(inputGraph logGraph): # Array to store constructed MST  parent = [0 for i in range(V)] # Key values used to pick minimum  key = [10000000 for i in range(V)] # weight edge in cut  # To represent set of vertices not  mstSet = [False for i in range(V)] # Yet included in MST  # Always include first 1st vertex in MST  # Make key 0 so that this vertex is  key[0] = 0 # Picked as first vertex  # First node is always root of MST  parent[0] = -1 # The MST will have V vertices  for count in range(0 V - 1): # Pick the minimum key vertex from # the set of vertices not yet  # included in MST  u = minKey(key mstSet) # Add the picked vertex to the MST Set  mstSet[u] = True # Update key value and parent index # of the adjacent vertices of the  # picked vertex. Consider only those  # vertices which are not yet  # included in MST  for v in range(V): # logGraph[u][v] is non zero only # for adjacent vertices of m  # mstSet[v] is false for vertices # not yet included in MST. Update  # the key only if logGraph[u][v] is  # smaller than key[v]  if (logGraph[u][v] > 0 and mstSet[v] == False and logGraph[u][v] < key[v]): parent[v] = u key[v] = logGraph[u][v] # Print the constructed MST  printMST(parent V inputGraph) # Method to get minimum product spanning tree  def minimumProductMST(graph): logGraph = [[0 for j in range(V)] for i in range(V)] # Constructing logGraph from  # original graph  for i in range(V): for j in range(V): if (graph[i][j] > 0): logGraph[i][j] = math.log(graph[i][j]) else: logGraph[i][j] = 0 # Applying standard Prim's MST algorithm # on Log graph.  primMST(graph logGraph) # Driver code if __name__=='__main__':    ''' Let us create the following graph   2 3   (0)--(1)--(2)   | /  |   6| 8/ 5 |7   | /  |   (3)-------(4)   9 ''' graph = [ [ 0 2 0 6 0 ] [ 2 0 3 8 5 ] [ 0 3 0 0 7 ] [ 6 8 0 0 9 ] [ 0 5 7 9 0 ] ] # Print the solution  minimumProductMST(graph) # This code is contributed by rutvik_56 
C#
// C# program for getting minimum product // spanning tree The program is for adjacency matrix // representation of the graph using System; class GFG {  // Number of vertices in the graph  static int V = 5;  // A utility function to find the vertex with minimum  // key value from the set of vertices not yet included  // in MST  static int minKey(int[] key Boolean[] mstSet)  {  // Initialize min value  int min = int.MaxValue min_index = 0;  for (int v = 0; v < V; v++) {  if (mstSet[v] == false && key[v] < min) {  min = key[v];  min_index = v;  }  }  return min_index;  }  // A utility function to print the constructed MST  // stored in parent[] and print Minimum Obtainable  // product  static void printMST(int[] parent int n int[ ] graph)  {  Console.Write('Edge Weightn');  int minProduct = 1;  for (int i = 1; i < V; i++) {  Console.Write('{0} - {1} {2} n'  parent[i] i graph[i parent[i]]);  minProduct *= graph[i parent[i]];  }  Console.Write('Minimum Obtainable product is {0}n'  minProduct);  }  // Function to construct and print MST for a graph  // represented using adjacency matrix representation  // inputGraph is sent for printing actual edges and  // logGraph is sent for actual MST operations  static void primMST(int[ ] inputGraph double[ ] logGraph)  {  int[] parent = new int[V]; // Array to store constructed MST  int[] key = new int[V]; // Key values used to pick minimum  // weight edge in cut  Boolean[] mstSet = new Boolean[V]; // To represent set of vertices not  // yet included in MST  // Initialize all keys as INFINITE  for (int i = 0; i < V; i++) {  key[i] = int.MaxValue;  mstSet[i] = false;  }  // Always include first 1st vertex in MST.  key[0] = 0; // Make key 0 so that this vertex is  // picked as first vertex  parent[0] = -1; // First node is always root of MST  // The MST will have V vertices  for (int count = 0; count < V - 1; count++) {  // Pick the minimum key vertex from the set of  // vertices not yet included in MST  int u = minKey(key mstSet);  // Add the picked vertex to the MST Set  mstSet[u] = true;  // Update key value and parent index of the  // adjacent vertices of the picked vertex.  // Consider only those vertices which are not yet  // included in MST  for (int v = 0; v < V; v++) // logGraph[u v] is non zero only for  // adjacent vertices of m mstSet[v] is false  // for vertices not yet included in MST  // Update the key only if logGraph[u v] is  // smaller than key[v]  {  if (logGraph[u v] > 0  && mstSet[v] == false  && logGraph[u v] < key[v]) {  parent[v] = u;  key[v] = (int)logGraph[u v];  }  }  }  // print the constructed MST  printMST(parent V inputGraph);  }  // Method to get minimum product spanning tree  static void minimumProductMST(int[ ] graph)  {  double[ ] logGraph = new double[V V];  // Constructing logGraph from original graph  for (int i = 0; i < V; i++) {  for (int j = 0; j < V; j++) {  if (graph[i j] > 0) {  logGraph[i j] = Math.Log(graph[i j]);  }  else {  logGraph[i j] = 0;  }  }  }  // Applying standard Prim's MST algorithm on  // Log graph.  primMST(graph logGraph);  }  // Driver code  public static void Main(String[] args)  {  /* Let us create the following graph  2 3  (0)--(1)--(2)  | /  |  6| 8/ 5 |7  | /  |  (3)-------(4)  9 */  int[ ] graph = {  { 0 2 0 6 0 }  { 2 0 3 8 5 }  { 0 3 0 0 7 }  { 6 8 0 0 9 }  { 0 5 7 9 0 }  };  // Print the solution  minimumProductMST(graph);  } } /* This code contributed by PrinciRaj1992 */ 
JavaScript
<script> // A Javascript program for getting minimum product // spanning tree The program is for adjacency matrix // representation of the graph // Number of vertices in the graph let V = 5; // A utility function to find the vertex with minimum  // key value from the set of vertices not yet included  // in MST function minKey(keymstSet) {  // Initialize min value  let min = Number.MAX_VALUE min_index = 0;    for (let v = 0; v < V; v++) {  if (mstSet[v] == false && key[v] < min) {  min = key[v];  min_index = v;  }  }  return min_index; } // A utility function to print the constructed MST  // stored in parent[] and print Minimum Obtainable  // product function printMST(parentngraph) {  document.write('Edge Weight  
'
); let minProduct = 1; for (let i = 1; i < V; i++) { document.write( parent[i]+' - '+ i+' ' +graph[i][parent[i]]+'
'
); minProduct *= graph[i][parent[i]]; } document.write('Minimum Obtainable product is ' minProduct+'
'
); } // Function to construct and print MST for a graph // represented using adjacency matrix representation // inputGraph is sent for printing actual edges and // logGraph is sent for actual MST operations function primMST(inputGraphlogGraph) { let parent = new Array(V); // Array to store constructed MST let key = new Array(V); // Key values used to pick minimum // weight edge in cut let mstSet = new Array(V); // To represent set of vertices not // yet included in MST // Initialize all keys as INFINITE for (let i = 0; i < V; i++) { key[i] = Number.MAX_VALUE; mstSet[i] = false; } // Always include first 1st vertex in MST. key[0] = 0; // Make key 0 so that this vertex is // picked as first vertex parent[0] = -1; // First node is always root of MST // The MST will have V vertices for (let count = 0; count < V - 1; count++) { // Pick the minimum key vertex from the set of // vertices not yet included in MST let u = minKey(key mstSet); // Add the picked vertex to the MST Set mstSet[u] = true; // Update key value and parent index of the // adjacent vertices of the picked vertex. // Consider only those vertices which are not yet // included in MST for (let v = 0; v < V; v++) // logGraph[u][v] is non zero only for // adjacent vertices of m mstSet[v] is false // for vertices not yet included in MST // Update the key only if logGraph[u][v] is // smaller than key[v] { if (logGraph[u][v] > 0 && mstSet[v] == false && logGraph[u][v] < key[v]) { parent[v] = u; key[v] = logGraph[u][v]; } } } // print the constructed MST printMST(parent V inputGraph); } // Method to get minimum product spanning tree function minimumProductMST(graph) { let logGraph = new Array(V); // Constructing logGraph from original graph for (let i = 0; i < V; i++) { logGraph[i]=new Array(V); for (let j = 0; j < V; j++) { if (graph[i][j] > 0) { logGraph[i][j] = Math.log(graph[i][j]); } else { logGraph[i][j] = 0; } } } // Applying standard Prim's MST algorithm on // Log graph. primMST(graph logGraph); } // Driver code /* Let us create the following graph 2 3 (0)--(1)--(2) | / | 6| 8/ 5 |7 | / | (3)-------(4) 9 */ let graph = [ [ 0 2 0 6 0 ] [ 2 0 3 8 5 ] [ 0 3 0 0 7 ] [ 6 8 0 0 9 ] [ 0 5 7 9 0 ] ]; // Print the solution minimumProductMST(graph); // This code is contributed by rag2127 </script>

Ieșire:  

Edge Weight 0 - 1 2 1 - 2 3 0 - 3 6 1 - 4 5 Minimum Obtainable product is 180

The complexitatea timpului al acestui algoritm este O(V2), deoarece există două bucle for imbricate care iterează peste toate vârfurile. 

The al acestui algoritm este O(V2), deoarece folosim o matrice 2-D de dimensiunea V x V pentru a stoca graficul de intrare.


 

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