chore(Java): add random node in linked list (#641)

algorithms/Java/Maths/algorithms_random_node.java

@@ -0,0 +1,92 @@
+/** Author : Suraj Kumar
+ * Github : https://github.com/skmodi649
+ */
+
+/** PROBLEM DESCRIPTION :
+ * There is a single linked list and we are supposed to find a random node in the given linked list
+  */
+
+/** ALGORITHM :
+ * Step 1 : START
+ * Step 2 : Create an arraylist of type integer
+ * Step 3 : Declare an integer type variable for size and linked list type for head
+ * Step 4 : We will use two methods, one for traversing through the linked list using while loop and also increase the size by 1
+ *
+ * (a) Algorithms_random_node(head)
+ * (b) run a while loop till null;
+ * (c) add the value to arraylist;
+ * (d) increase the size;
+ *
+ * Step 5 : Now use another method for getting random values using Math.random() and return the value present in arraylist for the calculated index
+ * Step 6 : Now in main() method we will simply insert nodes in the linked list and then call the appropriate method and then print the random node generated
+ * Step 7 : STOP
+ */
+
+package com.company;
+
+import java.util.ArrayList;
+
+public class Algorithms_random_node {
+
+    ArrayList<Integer> list;
+    int size;
+    static ListNode head;
+
+
+    static class ListNode{
+        int val;
+        ListNode next;
+
+        ListNode(int val){
+            this.val = val;
+        }
+    }
+    public Algorithms_random_node(ListNode head) {
+        list = new ArrayList<>();
+        size = 0;
+
+        ListNode temp = head;
+
+        //Now using while loop to traverse through the linked list and
+        //go on adding values and increasing the size value by 1
+
+        while (temp != null) {
+            list.add(temp.val);
+            temp=temp.next;
+            size++;
+        }
+    }
+
+    public int getRandom() {
+        int index = (int)(Math.random()*size);
+        return list.get(index);
+    }
+
+    // Driver program to test above functions
+    public static void main(String[] args) {
+
+
+        head = new ListNode(15);
+        head.next = new ListNode(25);
+        head.next.next = new ListNode(4);
+        head.next.next.next = new ListNode(1);
+        head.next.next.next.next = new ListNode(78);
+        head.next.next.next.next.next = new ListNode(63);
+        Algorithms_random_node list = new Algorithms_random_node(head);
+
+        int random_num = list.getRandom();
+        System.out.println("Random Node : "+random_num);
+    }
+}
+
+
+/** OUTPUT :
+ * First output :
+ * Random Node : 25
+ * Second output :
+ * Random Node : 78
+ */
+
+/** Time Complexity : O(n)
+ * Auxiliary Space Complexity : O(1)
+ */

algorithms/Java/README.md

@@ -31,6 +31,7 @@
 - [Factorial](Maths/factorial_using_big_integer.java)
 - [Catalan Numbers](Maths/catalan-numbers.java)
 - [Nth Geek Onacci Number](Maths/nth-geek-onacci-number.java)
+- [Random Node in Linked List](Maths/algorithms_random_node.java)
 
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