added delete-node-in-a-bst.java code

Author: pranav-3005

Coding/Java/delete-node-in-a-bst.java

@@ -0,0 +1,85 @@
+// question link : https://leetcode.com/problems/delete-node-in-a-bst/description/
+class Solution {
+
+    //1.reach the given node using recursion,if not found just return
+    public TreeNode deleteNode(TreeNode root, int val) {
+			if(root==null)
+				return root;
+
+            
+			if(val==root.val)
+			{//2. After found, there are 4 conditions
+                    
+                //2.1 cur node have both left & ryt nodes.  
+				if(root.left!=null && root.right!=null)
+				{
+					
+                    /*concept : take ryt node's left subtree,
+                                connect it to left node's ryt most node
+                                connect the updated left node to ryt node's left (i.e.. ryt.left=left)
+                                and return the updated ryt node. (deleting the cur node)
+                    */ 
+					
+					TreeNode ryt=cleft(root.left,root.right);
+					return ryt;
+				}
+
+                //2.2 have only ryt node
+				else if(root.left==null && root.right!=null)
+				{
+					return root.right;
+				}
+
+                //2.3 have only left node
+				else if(root.left!=null && root.right==null)
+				{
+					return root.left;
+				}
+
+                //2.4 have no child nodes.
+				else
+				{
+					return null;
+				}
+			}
+
+			if(val<root.val)
+			{
+				root.left=deleteNode(root.left,val);
+				return root;
+			}
+			else
+			{
+				root.right=deleteNode(root.right,val);
+				return root;
+			}
+    }
+
+    //cleft() -> does insert() func and connect the updated left to (ryt.left)
+    TreeNode cleft(TreeNode left,TreeNode ryt)
+	{
+		if(ryt.left==null)
+		{
+			ryt.left=left;
+			return ryt;
+		}
+		TreeNode temp=ryt.left;
+		ryt.left=insert(left,temp);
+		return ryt;
+		
+	}
+
+    //insert() -> connect ryt node's left subtree(temp) to rytmost of left node and return the updated left node
+    TreeNode insert(TreeNode root,TreeNode temp)
+	{
+		if(root==null)
+			return temp;
+		
+		root.right=insert(root.right,temp);
+
+		return root;
+	}
+	
+	
+
+}