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ShortestPath_undirectedGraph_withUnitWeights.java

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+package Graph;
+import java.util.*;
+
+/**
+ * Input : Given an undirected graph and a source node. We have to calculate the shortest distance from the given
+ *         source node to all the nodes present in the graph.
+ * Output :
+ * Distances of all nodes from the source node 1 are as following:
+ * Distance of node 1 from source node 1 is : 0
+ * Distance of node 2 from source node 1 is : 1
+ * Distance of node 3 from source node 1 is : 2
+ * Distance of node 4 from source node 1 is : 1
+ * Distance of node 5 from source node 1 is : 2
+ * Distance of node 6 from source node 1 is : 3
+ * Distance of node 7 from source node 1 is : 3
+ * Distance of node 8 from source node 1 is : 4
+ * Distance of node 9 from source node 1 is : 4
+ */
+public class ShortestPath_undirectedGraph_withUnitWeights {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        ArrayList<ArrayList<Integer>> adjacencyList = new ArrayList<>();
+
+        // Taking input for number of nodes
+        System.out.println("Enter the number of nodes:");
+        int numberOfNodes = sc.nextInt();
+
+        // initializing adjacencyList with new ArrayList<>()
+        for(int i=1 ; i<=numberOfNodes+1 ; i++){
+            adjacencyList.add(new ArrayList<>());
+        }
+
+        // taking input of adjacent nodes of particular node
+        for(int i=1 ; i<=numberOfNodes ; i++){
+            System.out.println("Enter number of adjacent nodes to the node : " + i);
+            int countOfAdjacentNodes = sc.nextInt();
+
+            // taking input of the particular adjacent nodes to the node i
+            System.out.println("Enter adjacent nodes:");
+            for(int j=0 ; j<countOfAdjacentNodes ; j++){
+
+                // taking input of adjacent node
+                int adjacentNode = sc.nextInt();
+                // adding the adjacent node to the particular node i
+                adjacencyList.get(i).add(adjacentNode);
+            }
+        }
+
+        int[] distance = new int[numberOfNodes+1];
+        Arrays.fill(distance, Integer.MAX_VALUE);
+
+        System.out.println("Enter the source node : ");
+        int sourceNode = sc.nextInt();
+
+        modifiedBFS(adjacencyList, sourceNode, distance);
+
+        System.out.println("Distances of all nodes from the source node " + sourceNode + " are as following: ");
+        for(int node=1 ; node<=numberOfNodes ; node++){
+            System.out.println("Distance of node " + node + " from source node " + sourceNode + " is : " + distance[node]);
+        }
+    }
+    public static void modifiedBFS(ArrayList<ArrayList<Integer>> adjacencyList, int sourceNode, int[] distance){
+        Queue<Integer> queue = new LinkedList<>();
+        queue.offer(sourceNode);
+        distance[sourceNode] = 0;
+
+        while (!queue.isEmpty()){
+            int currentNode = queue.poll();
+            for(int adjacentNode : adjacencyList.get(currentNode)){
+                if((distance[currentNode] + 1) < distance[adjacentNode]){
+                    distance[adjacentNode] = distance[currentNode] + 1;
+                    queue.offer(adjacentNode);
+                }
+            }
+        }
+    }
+}