Category: Sicp Solutions

Exercise 3.17.  Devise a correct version of the count-pairs procedure of exercise 3.16 that returns the number of distinct pairs in any structure. (Hint: Traverse the structure, maintaining an auxiliary data structure that is used to keep track of which pairs have already been counted.)   This file contains hidden or bidirectional Unicode text that may be…

Exercise 3.7.  Consider the bank account objects created by make-account, with the password modification described in exercise 3.3. Suppose that our banking system requires the ability to make joint accounts. Define a procedure make-joint that accomplishes this. Make-joint should take three arguments. The first is a password-protected account. The second argument must match the password with which…

Exercise 3.6.  It is useful to be able to reset a random-number generator to produce a sequence starting from a given value. Design a new rand procedure that is called with an argument that is either the symbol generate or the symbol reset and behaves as follows: (rand ‘generate) produces a new random number; ((rand ‘reset)…

Exercise 3.5.  Monte Carlo integration is a method of estimating definite integrals by means of Monte Carlo simulation. Consider computing the area of a region of space described by a predicate P(x, y) that is true for points (x, y) in the region and false for points not in the region. For example, the region contained…

Exercise 3.4.  Modify the make-account procedure of exercise 3.3 by adding another local state variable so that, if an account is accessed more than seven consecutive times with an incorrect password, it invokes the procedure call-the-cops. This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review,…

Exercise 3.3.  Modify the make-account procedure so that it creates password-protected accounts. That is, make-account should take a symbol as an additional argument, as in (define acc (make-account 100 ‘secret-password)) The resulting account object should process a request only if it is accompanied by the password with which the account was created, and should otherwise return a complaint: ((acc ‘secret-password ‘withdraw) 40) 60…

Exercise 3.2.  In software-testing applications, it is useful to be able to count the number of times a given procedure is called during the course of a computation. Write a procedure make-monitored that takes as input a procedure, f, that itself takes one input. The result returned by make-monitored is a third procedure, say mf, that…

Exercise 3.1.  An accumulator is a procedure that is called repeatedly with a single numeric argument and accumulates its arguments into a sum. Each time it is called, it returns the currently accumulated sum. Write a procedure make-accumulator that generates accumulators, each maintaining an independent sum. The input to make-accumulator should specify the initial value of…

Exercise 2.42.   Figure 2.8:  A solution to the eight-queens puzzle. The “eight-queens puzzle” asks how to place eight queens on a chessboard so that no queen is in check from any other (i.e., no two queens are in the same row, column, or diagonal). One possible solution is shown in figure 2.8. One way to solve the…

Exercise 2.59.  Implement the union-set operation for the unordered-list representation of sets. This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters ;; Exercise 2.59.…