我是LISP的初学者，我正在进行一项练习，要求我修改先呼吸，以便将其转换为统一成本搜索。
毋庸置疑，我非常困惑。我理解广度优先搜索和统一成本搜索如何工作的基础知识，但我无法实现它。
我有一些广度优先搜索的代码以及下面的节点和扩展方法的结构，但我在开发统一成本搜索时遇到了麻烦。
我知道它应该采用成本最低的路径，但我不确定如何实现它。我不太了解在整个地图上工作时应该如何保存所有这些路径和边缘（我正在使用的地图是罗马尼亚路线图，我确定谷歌将提出一份副本）
无论如何，我到目前为止的代码如下：
;The Problem:
setq ex2 '(
(Arad ( (Zerind 75) (Sibiu 140) (Timisoara 118) ) )
(Oradea ( (Zerind 71) (Sibiu 151) ) )
(Zerind ( (Oradea 71) (Arad 75) ) )
(Timisoara ( (Lugoj 111) (Arad 118) ) )
(Lugoj ( (Timisoara 111) (Medhadia 70) ) )
(Mehadia ( (Lugoj 70) (Drobeta 75) ) )
(Drobeta ( (Mehadia 75) (Craiova 120) ) )
(Sibiu ( (Oradea 151) (Arad 140) (Rimnicu-Vilcea 80) (Fagaras 99) ) )
(Rimnicu-Vilcea ( (Sibiu 80) (Craiova 146) (Pitesti 97) ) )
(Craiova ( (Rimnicu-Vilcea 146) (Drobeta 120) (Pitesti 138) ) )
(Fagaras ( (Sibiu 99) (Bucharest 211) ) )
(Pitesti ( (Rimnicu-Vilcea 97) (Craiova 138) (Bucharest 101) ) )
(Bucharest ( (Fagaras 211) (Pitesti 101) (Giurgiu 90) (Urziceni 85) ) )
(Giurgiu ( (Bucharest 90) ) )
(Neami ( (Iasi 87) ) )
(Iasi ( (Neami 87) (Vasiui 92) ) )
(Vasiui ( (Iasi 92) (Urziceni 142) ) )
(Urziceni ( (Bucharest 85) (Hirsova 98) (Vasiui 142) ) )
(Hirsova ( (Urziceni 98) (Eforie 86) ) )
(Eforie ( (Hirsova 86) ) )
) )
(setq problem3 (list 'Arad 'Bucharest ex2))
;return the start state from a problem
(defun initial-state (problem)
(car problem))
; return the goal state from a problem
(defun goal-state (problem)
(cadr problem))
; return the successor list from a problem
(defun adj-list (problem)
(caddr problem))
; construct a node from a state and a parent state
(defun make-node (state parent value depth)
(list state parent value depth))
; get the state from a node
(defun get-state (node)
(car node))
; get the parent state from a node
(defun get-parent (node)
(cadr node))
; get the value from a node
(defun get-value (node)
(caddr node))
; get the depth from a node
(defun get-depth (node)
(cadddr node))
;determine if a node represents the goal of a problem
(defun goal-test (problem node)
(cond ((equal (goal-state problem) (get-state node)) T)
(T nil)))
; create a list of nodes which represents the states adjacent to the state represented by node
(defun expand (node problem)
(expand-aux node (cadr (assoc (get-state node) (adj-list problem))) nil ))
; helper function for expand
(defun expand-aux (node states L)
(cond ((null states) L)
(T (expand-aux node
(cdr states)
(append L (list (make-node (caar states)
(get-state node)
(+ (get-value node) (cadar states))
(+ (get-depth node) 1) )))))))
; recover the solution path from the final (goal) node and the list of expanded nodes
(defun solution (node nodes)
(solution-aux node nodes nil))
; helper function for solution
(defun solution-aux (node nodes L &aux temp)
(setq temp (parent node nodes))
(cond ((equal temp nil) (cons (get-state node) L))
(T (solution-aux temp nodes (cons (get-state node) L)))))
; find the parent node of a node in a list of nodes
(defun parent (node nodes)
(assoc (get-parent node) nodes))
; determine if a node's state is already the state of a node in nodes
(defun already-present (node nodes)
(cond ((assoc (get-state node) nodes) T)
(T nil)))
;;;;; Breadth-first Search ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun breadth (problem)
(breadth-aux problem ; the problem
(list (make-node (initial-state problem) nil 0 0)) ; the fringe list
nil)) ; the closed list
(defun breadth-aux (problem fringe closed)
(cond ((null fringe) ; no place else to look, so fail
'Failure)
((goal-test problem (car fringe)) ; we have reach the goal, so return solution
(solution (car fringe) closed))
((already-present (car fringe) closed) ; this state was already reached, so go
(breadth-aux problem ; on without processing it
(cdr fringe)
closed))
(T ; process this node and go on
(breadth-aux problem
(append (cdr fringe) (expand (car fringe) problem))
(cons (car fringe) closed)))))
;;;;;;; Uniform-cost Search ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun uniform-cost (problem)
(uniform-aux problem
(list (make-node (initial-state problem) nil 0 0))
nil))
(defun uniform-aux (problem fringe closed)
(cond ((null fringe) 'Failure)
((goal-test problem (car fringe))
(solution (car fringe) closed))
((already-present (car fringe) closed)
(uniform-aux problem (cdr fringe) closed))
(T (uniform-aux problem
(append (cdr fringe) (expand
(car fringe)
problem))
(cons (car fringe) closed)))))