Added leetcode questions

Java/Count_Operations_to_Obtain_Zero.java

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+/*
+   LEETCODE QUESTION : 2169. Count Operations to Obtain Zero
+ */
+
+public class Count_Operations_to_Obtain_Zero {
+
+    public int countOperations(int num1, int num2) {
+        return helper(num1, num2, 0);
+
+    }
+
+    private int helper(int num1, int num2, int count) {
+
+        if (num1 == 0 || num2 == 0) {
+            return count;
+        }
+        if (num1 > num2)
+            return helper(num1 - num2, num2, count + 1);
+        else
+            return helper(num1, num2 - num1, count + 1);
+
+    }
+
+}

Java/Determine_Color_of_a_Chessboard_Square.java

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+/*
+   LEETCODE QUESTION : 1812. Determine Color of a Chessboard Square
+
+ */
+
+public class Determine_Color_of_a_Chessboard_Square {
+
+    public boolean squareIsWhite(String coordinates) {
+
+        int a = coordinates.charAt(0);
+        int b = coordinates.charAt(1);
+        if ((a + b) % 2 == 0) {
+            return false;
+        } else
+            return true;
+
+    }
+
+}

Java/Find_Greatest_Common_Divisor_of_Array.java

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+/*
+
+LEETCODE QUESTION : 1979. Find Greatest Common Divisor of Array
+
+=> Given an integer array nums, return the greatest common divisor of the smallest number and largest number in nums.
+    The greatest common divisor of two numbers is the largest positive integer that evenly divides both numbers.
+ */
+
+//The code
+class Find_Greatest_Common_Divisor_of_Array {
+    public int findGCD(int[] nums) {
+        insertion(nums);
+
+        int large = nums[nums.length - 1];
+        int small = nums[0];
+
+        int rem = large % small;
+
+        if (rem == 0) {
+            return small;
+        } else
+            return gcd(small, large);
+
+    }
+
+    static int gcd(int a, int b) {
+        int result = Math.min(a, b); // Find Minimum of a and b
+        while (result > 0) {
+            if (a % result == 0 && b % result == 0) {
+                break;
+            }
+            result--;
+        }
+        return result; // return gcd of a and b
+    }
+
+    private void insertion(int arr[]) {
+
+        for (int i = 0; i < arr.length - 1; i++) {
+
+            for (int j = i + 1; j > 0; j--) {
+
+                if (arr[j] < arr[j - 1]) {
+                    // swap
+                    swaparray(arr, j, j - 1);
+                } else {
+                    break;
+                }
+            }
+        }
+    }
+
+    static void swaparray(int[] arr, int first, int second) {
+
+        int temp = arr[first];
+        arr[first] = arr[second];
+        arr[second] = temp;
+
+    }
+
+}

Java/Linked List/Linked_List_Cycle.java

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+/*
+  LEETCODE QUESTION : 141. Linked List Cycle
+
+  => There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally, 
+     pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter.
+    Return true if there is a cycle in the linked list. Otherwise, return false.
+
+ */
+
+// * Definition for singly-linked list.
+public class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode() {
+    }
+
+    ListNode(int val) {
+        this.val = val;
+    }
+
+public class Linked_List_Cycle {
+    public boolean hasCycle(ListNode head) {
+        ListNode fast = head;
+        ListNode slow = head;
+
+        //for iteration 
+        while(fast!=null && fast.next!=null){
+            fast=fast.next.next;   //iterate 2 times
+            slow = slow.next;       //iterate 1 time
+
+            if(slow== fast)
+                return true;
+
+        }
+        return false;
+
+
+    }
+
+}

Java/Linked List/Middle_of_the_Linked_List.java

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+/*
+  LEETCODE QUESTION : 876. Middle of the Linked List
+  => Given the head of a singly linked list, return the middle node of the linked list.
+     If there are two middle nodes, return the second middle node.
+
+
+ */
+
+// * Definition for singly-linked list.
+public class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode() {
+    }
+
+    ListNode(int val) {
+        this.val = val;
+    }
+
+
+public class Middle_of_the_Linked_List {
+
+    //Add code from here in Leetcode.
+    public ListNode middleNode(ListNode head) {
+
+        ListNode fast = head;
+        ListNode slow = head;
+
+        while(fast!= null && fast.next != null){
+
+            slow=slow.next;
+            fast= fast.next.next;
+            //length=lenght+1;
+
+        }
+        return slow;
+
+
+
+    }
+
+}

Java/Linked List/Reverse_Linked_List.java

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+/*
+  LEETCODE QUESTION : 206. Reverse Linked List
+  => Given the head of a singly linked list, reverse the list, and return the reversed list.
+ */
+
+
+ // * Definition for singly-linked list.
+public class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode() {
+    }
+
+    ListNode(int val) {
+        this.val = val;
+    }
+
+    ListNode(int val, ListNode next) {
+        this.val = val;
+        this.next = next;
+    }
+}
+
+public class Reverse_Linked_List {
+
+    //Submit in leetcode from here :-
+    public ListNode reverseList(ListNode head) {
+        if (head == null) {
+            return head;
+        }
+        ListNode prev = null;
+        ListNode present = head;
+        ListNode nextnode = present.next;
+
+        while (present != null) {
+            present.next = prev;
+            prev = present;
+            present = nextnode;
+            if (nextnode != null) {
+                nextnode = nextnode.next;
+            }
+        }
+        return prev;
+
+    }
+
+}