diff --git a/DIRECTORY.md b/DIRECTORY.md
index 50f70abb2ed7..833062d17d42 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -852,6 +852,7 @@
* [KosarajuTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/KosarajuTest.java)
* [KruskalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/KruskalTest.java)
* [MatrixGraphsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/MatrixGraphsTest.java)
+ * [PrimMSTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/PrimMSTTest.java)
* [TarjansAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/TarjansAlgorithmTest.java)
* [WelshPowellTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/WelshPowellTest.java)
* hashmap
diff --git a/src/main/java/com/thealgorithms/datastructures/graphs/PrimMST.java b/src/main/java/com/thealgorithms/datastructures/graphs/PrimMST.java
index 7e11862786f6..8017c18ce6ac 100644
--- a/src/main/java/com/thealgorithms/datastructures/graphs/PrimMST.java
+++ b/src/main/java/com/thealgorithms/datastructures/graphs/PrimMST.java
@@ -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 @@ int minKey(int[] key, Boolean[] mstSet) {
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 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];
+ // 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
- // 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 @@ void primMST(int[][] graph) {
}
}
- // 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
}
}
diff --git a/src/test/java/com/thealgorithms/datastructures/graphs/PrimMSTTest.java b/src/test/java/com/thealgorithms/datastructures/graphs/PrimMSTTest.java
new file mode 100644
index 000000000000..ec59a3880642
--- /dev/null
+++ b/src/test/java/com/thealgorithms/datastructures/graphs/PrimMSTTest.java
@@ -0,0 +1,54 @@
+package com.thealgorithms.datastructures.graphs;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class PrimMSTTest {
+
+ private final PrimMST primMST = new PrimMST();
+
+ @Test
+ public void testSimpleGraph() {
+ // Test graph with 5 nodes and weighted edges
+ 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}};
+
+ int[] expectedParent = {-1, 0, 1, 0, 1};
+ int[] actualParent = primMST.primMST(graph);
+
+ assertArrayEquals(expectedParent, actualParent);
+ }
+
+ @Test
+ public void testDisconnectedGraph() {
+ // Test case with a disconnected graph (no valid MST)
+ int[][] graph = {{0, 1, 0, 0, 0}, {1, 0, 2, 0, 0}, {0, 2, 0, 3, 0}, {0, 0, 3, 0, 4}, {0, 0, 0, 4, 0}};
+
+ int[] expectedParent = {-1, 0, 1, 2, 3}; // Expected MST parent array
+ int[] actualParent = primMST.primMST(graph);
+
+ assertArrayEquals(expectedParent, actualParent);
+ }
+
+ @Test
+ public void testAllEqualWeightsGraph() {
+ // Test case where all edges have equal weight
+ int[][] graph = {{0, 1, 1, 1, 1}, {1, 0, 1, 1, 1}, {1, 1, 0, 1, 1}, {1, 1, 1, 0, 1}, {1, 1, 1, 1, 0}};
+
+ int[] expectedParent = {-1, 0, 0, 0, 0}; // Expected MST parent array (any valid spanning tree)
+ int[] actualParent = primMST.primMST(graph);
+
+ assertArrayEquals(expectedParent, actualParent);
+ }
+
+ @Test
+ public void testSparseGraph() {
+ // Test case with a sparse graph (few edges)
+ int[][] graph = {{0, 1, 0, 0, 0}, {1, 0, 1, 0, 0}, {0, 1, 0, 1, 0}, {0, 0, 1, 0, 1}, {0, 0, 0, 1, 0}};
+
+ int[] expectedParent = {-1, 0, 1, 2, 3}; // Expected MST parent array
+ int[] actualParent = primMST.primMST(graph);
+
+ assertArrayEquals(expectedParent, actualParent);
+ }
+}
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