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Graph : a diagram showing the relation between variable quantities, typically of two variables, each measured along one of a pair of axes at right angles.

Tree : a woody perennial plant, typically having a single stem or trunk growing to a considerable height and bearing lateral branches at some distance from the ground.

But how can we relate Tree in Computer Science !

Tree and graphs are datastructures having representation like trees(with root and leaf nodes)and graph (nodes and links) respectively.

Tree example : Graph example : A Tree is just a restricted form of a Graph.

Difference between Trees and Graphs

Trees Graphs
Path Tree is special form of graph i.e.
minimally connected graph and
having only one path between any two vertices.
In graph there can be more
than one path i.e. graph can have
uni-directional or bi-directional paths (edges)
between nodes
Loops Tree is a special case of graph having no loops, no circuitsand no self-loops. Graph can have loops,
circuits as well as can have self-loops.
Root Node In tree there is exactly one root node and
every child have only one parent.
In graph there is no such concept of
root node.
Parent Child relationship In trees, there is parent child relationship
so flow can be there with direction
top to bottom or vice versa.
In Graph there is no such parent
child relationship.
Complexity Trees are less complex then graphs as
having no cycles, no self-loops and still connected.
Graphs are more complex in
compare to trees as it can have cycles, loops etc
Types of Traversal Tree traversal is a kind of special case of
traversal of graph. Tree is traversed in Pre-OrderIn-Order and Post-Order(all three in DFS or in BFS algorithm)
Graph is traversed by
DFS: Depth First Search and in
BFS : Breadth First Search algorithm
Connection Rules In trees, there are many rules / restrictions for making connections between nodes through edges. In graphs no such rules/ restrictions
are there for connecting the nodes
through edges.
DAG Trees come in the category of DAG :
Directed Acyclic Graphs
is a kind of directed graph that have no cycles.
Graph can be Cyclic or Acyclic.
Different Types Different types of trees are :
Binary Tree , Binary Search Tree, AVL tree, Heaps
.
There are mainly two types of Graphs :
Directed and Undirected graphs.
Applications Tree applications : sorting and searching like Tree Traversal & Binary Search. Graph applications :
Coloring of maps, in OR (PERT & CPM), algorithms, Graph coloring, job scheduling, etc.
No. of edges Tree always has n-1 edges. In Graph, no. of edges depend on the graph.
Model Tree is a hierarchical model. Graph is a network model.
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Difference in Coding Formats ?

There is no change in coding format but there is change in logic the way programs are written.

The thing is first understand what actually a tree is or what actually a graph is

For coding practices below are the references you should check out :