From 07f97cf9361993d0523de8fe8e255ffb1dfe3fdd Mon Sep 17 00:00:00 2001
From: Amal Bijoy <amalbijoy2007@gmail.com>
Date: Tue, 7 Apr 2026 11:34:35 +0530
Subject: [PATCH] Add edge removal and bounds validation for graph demos

---
 Data-Structures/Graphs/AdjacencyList.java   | 50 +++++++++++++++------
 Data-Structures/Graphs/AdjacencyMatrix.java | 49 ++++++++++++++------
 2 files changed, 72 insertions(+), 27 deletions(-)

diff --git a/Data-Structures/Graphs/AdjacencyList.java b/Data-Structures/Graphs/AdjacencyList.java
index 29f7695..9eaa4d4 100644
--- a/Data-Structures/Graphs/AdjacencyList.java
+++ b/Data-Structures/Graphs/AdjacencyList.java
@@ -1,11 +1,27 @@
 import java.util.*;
 
-public class AdjacencyList {
-
-    public static void addEdge(List<List<Integer>> adj, int i, int j) {
-        adj.get(i).add(j);
-        adj.get(j).add(i); // for undirected graph
-    }
+public class AdjacencyList {
+    private static void validateVertex(List<List<Integer>> adj, int vertex, String name) {
+        if (vertex < 0 || vertex >= adj.size()) {
+            throw new IllegalArgumentException(
+                name + " index out of bounds: " + vertex + ". Valid range is 0 to " + (adj.size() - 1)
+            );
+        }
+    }
+
+    public static void addEdge(List<List<Integer>> adj, int i, int j) {
+        validateVertex(adj, i, "Source vertex");
+        validateVertex(adj, j, "Destination vertex");
+        adj.get(i).add(j);
+        adj.get(j).add(i); // for undirected graph
+    }
+
+    public static void removeEdge(List<List<Integer>> adj, int i, int j) {
+        validateVertex(adj, i, "Source vertex");
+        validateVertex(adj, j, "Destination vertex");
+        adj.get(i).remove(Integer.valueOf(j));
+        adj.get(j).remove(Integer.valueOf(i)); // for undirected graph
+    }
 
     public static void displayAdjList(List<List<Integer>> adj) {
         for (int i = 0; i < adj.size(); i++) {
@@ -26,11 +42,17 @@ public static void main(String[] args) {
         }
 
         addEdge(adj, 0, 1);
-        addEdge(adj, 0, 2);
-        addEdge(adj, 1, 2);
-        addEdge(adj, 2, 3);
-
-        System.out.println("Adjacency List Representation:");
-        displayAdjList(adj);
-    }
-}
+        addEdge(adj, 0, 2);
+        addEdge(adj, 1, 2);
+        addEdge(adj, 2, 3);
+
+        System.out.println("Adjacency List after adding edges:");
+        displayAdjList(adj);
+
+        removeEdge(adj, 1, 2);
+        removeEdge(adj, 2, 3);
+
+        System.out.println("Adjacency List after removing edges (1,2) and (2,3):");
+        displayAdjList(adj);
+    }
+}
diff --git a/Data-Structures/Graphs/AdjacencyMatrix.java b/Data-Structures/Graphs/AdjacencyMatrix.java
index 1fe9950..d514693 100644
--- a/Data-Structures/Graphs/AdjacencyMatrix.java
+++ b/Data-Structures/Graphs/AdjacencyMatrix.java
@@ -1,8 +1,25 @@
-public class AdjacencyMatrix {
-    public static void addEdge(int[][] mat, int i, int j) {
-        mat[i][j] = 1;
-        mat[j][i] = 1; // for undirected graph
-    }
+public class AdjacencyMatrix {
+    private static void validateVertex(int[][] mat, int vertex, String name) {
+        if (vertex < 0 || vertex >= mat.length) {
+            throw new IllegalArgumentException(
+                name + " index out of bounds: " + vertex + ". Valid range is 0 to " + (mat.length - 1)
+            );
+        }
+    }
+
+    public static void addEdge(int[][] mat, int i, int j) {
+        validateVertex(mat, i, "Source vertex");
+        validateVertex(mat, j, "Destination vertex");
+        mat[i][j] = 1;
+        mat[j][i] = 1; // for undirected graph
+    }
+
+    public static void removeEdge(int[][] mat, int i, int j) {
+        validateVertex(mat, i, "Source vertex");
+        validateVertex(mat, j, "Destination vertex");
+        mat[i][j] = 0;
+        mat[j][i] = 0; // for undirected graph
+    }
 
     public static void displayMatrix(int[][] mat) {
         for (int[] row : mat) {
@@ -18,11 +35,17 @@ public static void main(String[] args) {
         int[][] mat = new int[v][v];
 
         addEdge(mat, 0, 1);
-        addEdge(mat, 0, 2);
-        addEdge(mat, 1, 2);
-        addEdge(mat, 2, 3);
-
-        System.out.println("Adjacency Matrix Representation:");
-        displayMatrix(mat);
-    }
-}
+        addEdge(mat, 0, 2);
+        addEdge(mat, 1, 2);
+        addEdge(mat, 2, 3);
+
+        System.out.println("Adjacency Matrix after adding edges:");
+        displayMatrix(mat);
+
+        removeEdge(mat, 1, 2);
+        removeEdge(mat, 2, 3);
+
+        System.out.println("Adjacency Matrix after removing edges (1,2) and (2,3):");
+        displayMatrix(mat);
+    }
+}