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Enhance docs, remove main, add tests in PrimMST (#5969)

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Hardik Pawar
2024-10-26 23:40:19 +05:30
committed by GitHub
parent ce3dd01e68
commit 62c9309a31
3 changed files with 72 additions and 66 deletions
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83
src/main/java/com/thealgorithms/datastructures/graphs/PrimMST.java
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@ -1,19 +1,17 @@
package com.thealgorithms.datastructures.graphs;
/**
* A Java program for Prim's Minimum Spanning Tree (MST) algorithm. adjacency
* matrix representation of the graph
* A Java program for Prim's Minimum Spanning Tree (MST) algorithm.
* Adjacency matrix representation of the graph.
*/
class PrimMST {
public class PrimMST {
// 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
// A utility function to find the vertex with the minimum key
// value, from the set of vertices not yet included in the MST
int minKey(int[] key, Boolean[] mstSet) {
// Initialize min value
int min = Integer.MAX_VALUE;
int minIndex = -1;
@ -27,54 +25,30 @@ class PrimMST {
return minIndex;
}
// A utility function to print the constructed MST stored in
// parent[]
void printMST(int[] parent, int n, int[][] graph) {
System.out.println("Edge Weight");
for (int i = 1; i < V; i++) {
System.out.println(parent[i] + " - " + i + " " + graph[i][parent[i]]);
}
}
// Function to construct MST for a graph using adjacency matrix representation
public int[] primMST(int[][] graph) {
int[] parent = new int[V]; // Array to store constructed MST
int[] key = new int[V]; // Key values to pick minimum weight edge
Boolean[] mstSet = new Boolean[V]; // Vertices not yet included in MST
// 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 not yet included in MST
Boolean[] mstSet = new Boolean[V];
// Initialize all keys as INFINITE
// Initialize all keys as INFINITE and mstSet[] as false
for (int i = 0; i < V; i++) {
key[i] = Integer.MAX_VALUE;
mstSet[i] = Boolean.FALSE;
}
// Always include first 1st vertex in MST.
key[0] = 0; // Make key 0 so that this vertex is
// picked as first vertex
// Always include the first vertex in MST
key[0] = 0; // Make key 0 to pick the 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
// Pick the minimum key vertex not yet included in MST
int u = minKey(key, mstSet);
// Add the picked vertex to the MST Set
mstSet[u] = Boolean.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++) // Update the key only if graph[u][v] is smaller than key[v] // mstSet[v] is
// false for vertices not yet included in MST // graph[u][v] is non zero only
// for adjacent vertices of m
{
// Update key value and parent index of adjacent vertices of the picked vertex
for (int v = 0; v < V; v++) {
if (graph[u][v] != 0 && !mstSet[v] && graph[u][v] < key[v]) {
parent[v] = u;
key[v] = graph[u][v];
@ -82,29 +56,6 @@ class PrimMST {
}
}
// print the constructed MST
printMST(parent, V, 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 */
PrimMST t = new PrimMST();
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);
return parent; // Return the MST parent array
}
}