def backtracking_search(csp,
                        select_unassigned_variable = first_unassigned_variable,
                        order_domain_values = unordered_domain_values,
                        inference = no_inference):
    """[Fig. 6.5]
    >>> backtracking_search(australia) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv) is not None
    True
    >>> backtracking_search(australia, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, inference=forward_checking) is not None
    True
    >>> backtracking_search(australia, inference=mac) is not None
    True
    >>> backtracking_search(usa, select_unassigned_variable=mrv, order_domain_values=lcv, inference=mac) is not None
    True
    """

    def backtrack(assignment):
        if len(assignment) == len(csp.vars):
            return assignment
        var = select_unassigned_variable(assignment, csp)
        for value in order_domain_values(var, assignment, csp):
            if 0 == csp.nconflicts(var, value, assignment):
                csp.assign(var, value, assignment)
                removals = csp.suppose(var, value)
                if inference(csp, var, value, assignment, removals):
                    result = backtrack(assignment)
                    if result is not None:
                        return result
                csp.restore(removals)
        csp.unassign(var, assignment)
        return None

    result = backtrack({})
    assert result is None or csp.goal_test(result)
    return result
def backtracking_search(csp,
                        select_unassigned_variable = first_unassigned_variable,
                        order_domain_values = unordered_domain_values,
                        inference = no_inference):
    """[Fig. 6.5]
    >>> backtracking_search(australia) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv) is not None
    True
    >>> backtracking_search(australia, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, inference=forward_checking) is not None
    True
    >>> backtracking_search(australia, inference=mac) is not None
    True
    >>> backtracking_search(usa, select_unassigned_variable=mrv, order_domain_values=lcv, inference=mac) is not None
    True
    """

    def backtrack(assignment):
        if len(assignment) == len(csp.vars):
            return assignment
        var = select_unassigned_variable(assignment, csp)
        for value in order_domain_values(var, assignment, csp):
            if 0 == csp.nconflicts(var, value, assignment):
                csp.assign(var, value, assignment)
                removals = csp.suppose(var, value)
                if inference(csp, var, value, assignment, removals):
                    result = backtrack(assignment)
                    if result is not None:
                        return result
                csp.restore(removals)
        csp.unassign(var, assignment)
        return None

    result = backtrack({})
    assert result is None or csp.goal_test(result)
    return result
def backtracking_search ( csp , select_unassigned_variable = first_unassigned_variable , order_domain_values = unordered_domain_values , inference = no_inference ) : def backtrack ( assignment ) : if len ( assignment ) == len ( csp . vars ) : return assignment var = select_unassigned_variable ( assignment , csp ) for value in order_domain_values ( var , assignment , csp ) : if 0 == csp . nconflicts ( var , value , assignment ) : csp . assign ( var , value , assignment ) removals = csp . suppose ( var , value ) if inference ( csp , var , value , assignment , removals ) : result = backtrack ( assignment ) if result is not None : return result csp . restore ( removals ) csp . unassign ( var , assignment ) return None result = backtrack ( { } ) assert result is None or csp . goal_test ( result ) return result
[Fig. 6.5]
    >>> backtracking_search(australia) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv) is not None
    True
    >>> backtracking_search(australia, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, select_unassigned_variable=mrv, order_domain_values=lcv) is not None
    True
    >>> backtracking_search(australia, inference=forward_checking) is not None
    True
    >>> backtracking_search(australia, inference=mac) is not None
    True
    >>> backtracking_search(usa, select_unassigned_variable=mrv, order_domain_values=lcv, inference=mac) is not None
    True
[ Fig . 6 . 5 ] >>> backtracking_search ( australia ) is not None True >>> backtracking_search ( australia select_unassigned_variable = mrv ) is not None True >>> backtracking_search ( australia order_domain_values = lcv ) is not None True >>> backtracking_search ( australia select_unassigned_variable = mrv order_domain_values = lcv ) is not None True >>> backtracking_search ( australia inference = forward_checking ) is not None True >>> backtracking_search ( australia inference = mac ) is not None True >>> backtracking_search ( usa select_unassigned_variable = mrv order_domain_values = lcv inference = mac ) is not None True