A tree is a data structure that stores elements in a hierarchy.

• We refer to this elements as nodes and the lines that connect them as edges.
• The top node in the tree is called root.
• Root is parent of its child nodes(2,3).
• The nodes without any children is known as leaf nodes.

In this example our nodes have maximum of two children this is a special type of tree called Binary tree.

Applications

Binary Search Tree

Traversing Trees

Recursion

Recursion is the process of calling the method itself within the method.

• Base Condition: It is a way to terminate the recursion at one point. Without this condition, the recurrence will last forever.
• Java is going to remember these method calls one by one and return them in order using stacks. Everytime we give a recursive call, Java is going to keep track of the value of these variables in a stack.