Re: Recursion/Algorithm Question
Thanks, That (along with returning the completed path via (list)) nailed it. I thought I'd tried concat at some point, but that might have been with another problem I've been tackling. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Recursion/Algorithm Question
Thanks, Nathan, that did help. I'm still stuck, however, figuring out how to return the values as a flat sequence of vectors. Maybe I'm just missing the right function from the API. Here's where I'm at right now: (defn get-paths ([n] (get-paths n [0 0] '())) ([n point path] (cond (points-equal? (vector n n) point) (reverse (conj path point)) (out-of-bounds? n point) nil (blocked? point) nil :else (list (get-paths n (inc-y point) (conj path point)) (get-paths n (inc-x point) (conj path point)) So, right now when I call the function with nothing blocked (get-paths 1) it returns ((nil ([0 0] [0 1] [1 1])) (([0 0] [1 0] [1 1]) nil)) but what I want is (([0 0] [0 1] [1 1]) ([0 0] [1 0] [1 1])) so that a call to (count) would return the total number of paths. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Recursion/Algorithm Question
You're right on the doorstep again :) If you want to make a single, flat list out of two different lists, the function you're looking for is 'concat' You may find the cheat sheet helpful: http://clojure.org/cheatsheet. In this case you were looking for some operation on sequences which gave you a sequence back. There's a category for that on the sheet. It can save some time in narrowing down the docs you have to read through when you're just getting familiar with the core API. On Sep 22, 3:48 pm, ax2groin ax2gr...@gmail.com wrote: Thanks, Nathan, that did help. I'm still stuck, however, figuring out how to return the values as a flat sequence of vectors. Maybe I'm just missing the right function from the API. Here's where I'm at right now: (defn get-paths ([n] (get-paths n [0 0] '())) ([n point path] (cond (points-equal? (vector n n) point) (reverse (conj path point)) (out-of-bounds? n point) nil (blocked? point) nil :else (list (get-paths n (inc-y point) (conj path point)) (get-paths n (inc-x point) (conj path point)) So, right now when I call the function with nothing blocked (get-paths 1) it returns ((nil ([0 0] [0 1] [1 1])) (([0 0] [1 0] [1 1]) nil)) but what I want is (([0 0] [0 1] [1 1]) ([0 0] [1 0] [1 1])) so that a call to (count) would return the total number of paths. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Recursion/Algorithm Question
A recursive formulation is exactly the right idea. Also, you're right when you say it won't work with recur as you've set it up. In fact, you won't be able to use recur at all in this situation as a you are doing a depth-first search through possible paths--it's impossible to formulate a depth-first search as a tail-recursive function. You are definitely on the right track with your current idea. Though I would offer a hint: it's even simpler to return a sequence of all the paths (in a way very similar to how you've set it up) without using ANY of the state ref types. On Sep 21, 9:29 am, ax2groin ax2gr...@gmail.com wrote: I've been working through algorithm problems to learn the language a little better. I'm currently struggling with the question about a robot traversing a grid. If the grid is completely open, then the answer to how many possible ways to traverse the grid? is simply the math for combinations using factorials (see Project Euler #15). But if you suppose that some places in the grid are blocked or that you have to actually traverse the paths? I know that the code below doesn't work yet (recur is not at the tail). Think of it as pseudo-code to show my intent. I've left out the other methods to get at the heart of what I'm asking about. Essentially, each path leads to two more recursion points (at least the way I've formulated it in my else), until they finally run out of bounds or meet the goal. The input n represents the width of the square grid. I'm using a two-element vector to represent a point in the grid. (defn get-paths [n] (let [paths (agent '()) goal (vector n n)] (loop [point [0 0] path '()] (cond (points-equal? goal point) (send paths conj (conj path point)) (out-of-bounds? n point) nil (blocked? point) nil :else (recur (inc-x point) (conj path point)) (recur (inc-y point) (conj path point (deref paths))) Perhaps ultimately, the approach I've tried here is a dead-end? I'm not sure that this loop formulation would ever exit, or perhaps it would exit too quickly. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
