I need help with Dr.Racket (Scheme, Lisp).

I just have to Implement "find-solution using A* search". I don't know what it is I just know that it's a Heuristic-based and it combines DFS and Breath-First Search. Please help.

Main ideas of A* search . not every sequence needs to be explored . visited successors can be ignored . explore the most promising sequence first

ACCUMULATOR INVARIANTS: . paths is a list of all seqsstarting at b generated so far that have no repeated nodes . visited is the list of boards encountered on all sequences explored so far

However, below is an example of a Breath-First Search.

; find-solution-bfs: board --> seq

; Purpose: To find a solution to the given board

(define (find-solution-bfs b)

(local [; search-paths: lseq --> seq

; Purpose: To find a solution to b by searching all possible paths

; ACCUMULATOR INVARIANT: ; paths is all paths starting at b generated so far from shortest to longest (define (search-paths paths) (cond [(equal? (first (first paths)) WIN) (first paths)] [else (local [(define children (generate-children (first (first paths)))) (define new-paths (map (lambda (c) (cons c (first paths))) children))] (search-paths (append (rest paths) new-paths)))]))] (reverse (search-paths (list (list b))))))