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# Assignment 2 brute-force search algorithms

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FUNDAMENTALS OF ARTIFICIAL INTELLIGENCE – CS161
Programming Assignment 2 –
DO NOT CONSULT ANY OUTSIDE REFERENCES OR SOURCES FOR THIS PROBLEM SET
The problem is to implement several brute-force search algorithms, including
depth-first, breadth-first, and depth-first iterative-deepening. The search
trees will be represented as lists in which a leaf node is represented by an
atom, and a non-leaf node is represented by a list of its child nodes. For
example, the list ((W X) (Y Z)) represents the complete two-level binary tree
shown below on the left, and the list ((A (B)) C (D)) represents the tree shown
below on the right.
1. Write a single pure LISP function, called DFS, that performs a depth-first
search of a tree. The function should take a single argument that is the list
representation of the tree, and return a single, top-level list of the terminal
nodes in the order they would be visited by a left-to-right depth-first search.
For example, (dfs ‘((A (B)) C (D))) would return (A B C D). Do not use any
auxiliary functions.
2. Write a set of pure LISP functions that implement depth-first
iterative-deepening. Your top-level function, called DFID, should take two
arguments, the list representation of the tree, and an integer representing the
maximum depth of the tree, and return a single top-level list of the terminal
nodes in the order that they would be visited by a left-to-right depth-first
iterative-deepening search. Note that those nodes that are visited in multiple
iterations will appear multiple times in the output list. For example, (dfid
‘((A (B)) C (D)) 3) would return (C A C D A B C D).
3. Write a single pure LISP function, called BFS, that performs a breadth-first
search of a tree. The function should take a single argument that is the list
representation of the tree, and return a single, top-level list of the terminal
nodes in the order they would be visited by a left-to-right breadth-first
search. For example, (bfs ‘((A (B)) C (D))) would return (C A D B). Do not
use any auxiliary functions.
All your programs must work for trees of arbitrary depth and branching factor,
and hence you may not assume any a priori upper bound on these parameters. Be
sure to experiment with sufficient test cases to convince yourself that your
programs work in general.