Add Maximum Weighted Matching Algorithm for Trees (#6184)

src/main/java/com/thealgorithms/datastructures/graphs/UndirectedAdjacencyListGraph.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.datastructures.graphs;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class UndirectedAdjacencyListGraph {
+    private ArrayList<HashMap<Integer, Integer>> adjacencyList = new ArrayList<>();
+
+    /**
+     * Adds a new node to the graph by adding an empty HashMap for its neighbors.
+     * @return the index of the newly added node in the adjacency list
+     */
+    public int addNode() {
+        adjacencyList.add(new HashMap<>());
+        return adjacencyList.size() - 1;
+    }
+
+    /**
+     * Adds an undirected edge between the origin node (@orig) and the destination node (@dest) with the specified weight.
+     * If the edge already exists, no changes are made.
+     * @param orig the index of the origin node
+     * @param dest the index of the destination node
+     * @param weight the weight of the edge between @orig and @dest
+     * @return true if the edge was successfully added, false if the edge already exists or if any node index is invalid
+     */
+    public boolean addEdge(int orig, int dest, int weight) {
+        int numNodes = adjacencyList.size();
+        if (orig >= numNodes || dest >= numNodes || orig < 0 || dest < 0) {
+            return false;
+        }
+
+        if (adjacencyList.get(orig).containsKey(dest)) {
+            return false;
+        }
+
+        adjacencyList.get(orig).put(dest, weight);
+        adjacencyList.get(dest).put(orig, weight);
+        return true;
+    }
+
+    /**
+     * Returns the set of all adjacent nodes (neighbors) for the given node.
+     * @param node the index of the node whose neighbors are to be retrieved
+     * @return a HashSet containing the indices of all neighboring nodes
+     */
+    public HashSet<Integer> getNeighbors(int node) {
+        return new HashSet<>(adjacencyList.get(node).keySet());
+    }
+
+    /**
+     * Returns the weight of the edge between the origin node (@orig) and the destination node (@dest).
+     * If no edge exists, returns null.
+     * @param orig the index of the origin node
+     * @param dest the index of the destination node
+     * @return the weight of the edge between @orig and @dest, or null if no edge exists
+     */
+    public Integer getEdgeWeight(int orig, int dest) {
+        return adjacencyList.get(orig).getOrDefault(dest, null);
+    }
+
+    /**
+     * Returns the number of nodes currently in the graph.
+     * @return the number of nodes in the graph
+     */
+    public int size() {
+        return adjacencyList.size();
+    }
+}