Best first search is an informed search algorithm that traverses the search tree by choosing the most promising node first. It uses an evaluation function to determine which node to expand next based on estimated distance to the goal. It maintains an open list of generated nodes not yet expanded, sorted by estimated cost. At each step, it removes the node with lowest estimated cost from the open list and expands it, adding any generated successors to the open list. This allows it to combine benefits of breadth-first and depth-first search by prioritizing promising paths over less promising ones. An example is provided tracing the steps of best first search to find the goal nodes L and Z from the starting node C in a search tree.

1. GOVERNMENT COLLEGE OF ENGINEERING &
TEXTILE TECHNOLOGY, SERAMPORE
NAME-MUKTARUL HOQUE
STREAM-INFORMATION TECHNOLOGY
ROLL-11000220015
SUBJECT-ARTIFICIAL INTELLIGENCE

2. BEST FIRST SEARCH ALGORITHM
Guided By Mr. Biplab Mahapatra(State Aided College Teacher,IT
Depaerment)
Defination:
Best first search is a traversal technique that decides which node is to be
visited next by checking which node is the most promising one and then
check it. For this it uses an evaluation function to decide the traversal.
This best first search technique of tree traversal comes under the category
of heuristic search or informed search technique.
The cost of nodes is stored in a priority queue. This makes implementation
of best-first search is same as that of breadth First search. We will use the
priorityqueue just like we use a queue for BFS

3. PROCESS
We have studied two uninformed search algorithms such
as Breadth First search (BFS) and Depth First
search(DFS) Algorithm.
DFS is good because it allows a solution to be found
without all competing branches having to be expanded
BFS is good because it does not get branches on
dead-end paths
One way of combining the two is to follow a single path
at a time, but switch paths whenever some competing
path looks more promising than the current one does.

4. At each step of the BFS search process, we select
the most promising of the nodes we have
generated so far
.
This is done by applying an appropriate heuristic
function to each of them.
We then expand the chosen node by using the rules
to generate its successors
It proceeds in steps, expanding one node at each
step until it generates a node that corresponds to a
goal state.

5. At each step, it picks the most promising of the nodes
that have so far been generated but not expanded.
It generates the successors of the chosen node,
applies the heuristic function to them, and adds
them to the list of open nodes, after checking to see
if any of them have been generated before.

6. ALGORITHM: BEST-FIRST SEARCH
 1. Start with OPEN containing just the initial state
 2. Until a goal is found or there are no nodes left on
OPEN do:
a) Pick them best node on OPEN.
b) Generate its successors.
c) For each successor do:
i) if it has not been generated
before, evaluate it, add it to OPEN, and record its
parent.
ii) If it has been generated before,
change the parent if this new path is better than the
previous one. In that case, update the cost of getting to
this node and to any successors that this node may
already have.

7. EXAMPLE: BEST-FIRST SEARCH
Q.Here C is the initial or source node and L and Z are
goal nodes.
Open: C
Closed: —

8. Now, C is added to Closed, and B, T, O, E and P are
added to Open.
Open: T, O, E, B, P
Closed: C

9.  Now, T has the least distance hence, T is added to
Closed.
Open: O, E, B, P
Closed: C, T

10.  As T does not have any successors, the next node
from open that is O is removed from Open and
added to closed.
Open: E, B, P
Closed: C, T, O

11.  The successors of node O that is node I and N are
added to Open.
Open: I, E, B, P, N
Closed: C, T, O

12.  Now, node I is removed from Open and added to
closed.
Open: E, B, P, N
Closed: C, T, O, I

13.  The successor of I that is Z is added to Open.
Open: Z, E, B, P, N
Closed: C, T, O, I

14.  Now, node Z is removed from Open and added to
closed.
 Open: E, B, P, N
 Closed: C, T, O, I, Z
The Goal is found. The final path is C – O – I – Z.

15. CONCLUSION
1. Can switch between BFS and DFS, thus gaining
the advantages of both.
2. More efficient when compared to DFS.

16. REFERENCES
https://www.tutorialspoint.com/best-first-search-
informed-search
https://www.geeksforgeeks.org/best-first-search-
informed-search/
https://www.javatpoint.com/ai-informed-search-
algorithms

17. THANK YOU