Add PrimsAlgo.java

Program for Prim's Algorithm

Author: rajniarora26

PrimsAlgo.java

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+// A Java program for Prim's Minimum Spanning Tree (MST) algorithm.
+// The program is for adjacency matrix representation of the graph
+
+import java.util.*;
+import java.lang.*;
+import java.io.*;
+
+class PrimsAlgo {
+	// Number of vertices in the graph
+	private static final int 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[], Boolean mstSet[])
+	{
+		// Initialize min value
+		int min = Integer.MAX_VALUE, min_index = -1;
+
+		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[]
+	void printMST(int parent[], int graph[][])
+	{
+		System.out.println("Edge \tWeight");
+		for (int i = 1; i < V; i++)
+			System.out.println(parent[i] + " - " + i + "\t" + graph[i][parent[i]]);
+	}
+
+	// Function to construct and print MST for a graph represented
+	// using adjacency matrix representation
+	void primMST(int graph[][])
+	{
+		// Array to store constructed MST
+		int parent[] = new int[V];
+
+		// Key values used to pick minimum weight edge in cut
+		int key[] = new int[V];
+
+		// To represent set of vertices included in MST
+		Boolean mstSet[] = new Boolean[V];
+
+		// 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 thd 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++)
+
+				// graph[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 graph[u][v] is smaller than key[v]
+				if (graph[u][v] != 0 && mstSet[v] == false && graph[u][v] < key[v]) {
+					parent[v] = u;
+					key[v] = graph[u][v];
+				}
+		}
+
+		// print the constructed MST
+		printMST(parent, graph);
+	}
+
+	public static void main(String[] args)
+	{
+		/* Let us create the following graph
+		2 3
+		(0)--(1)--(2)
+		| / \ |
+		6| 8/ \5 |7
+		| /	 \ |
+		(3)-------(4)
+			9		 */
+		MST t = new MST();
+		int graph[][] = new int[][] { { 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
+		t.primMST(graph);
+	}
+}