Convert a given binary tree to Doubly Linked List

Converting a binary tree to a doubly linked list means transforming the given binary tree data structure into a linked list data structure in such a way that each node of the binary tree is represented as a node of the linked list, and the links between the nodes in the binary tree become the links between the nodes in the doubly linked list.

In a doubly linked list, each node has two pointers or references, one to the previous node and one to the next node. In a binary tree, each node has at most two child nodes, a left child and a right child.

The conversion process involves traversing the binary tree in a specific order, such as inorder, preorder, or postorder, and creating a doubly linked list by connecting the nodes in the order they are visited. The left child of a node becomes the previous node in the doubly linked list, and the right child becomes the next node.

The resulting doubly linked list will have its head pointing to the first node of the list, and its tail pointing to the last node of the list. This conversion can be useful in certain applications, such as implementing algorithms that require the traversal of a tree in a linear fashion.