tasks a-s

Task/Priority-queue/Maxima/priority-queue.maxima

@@ -0,0 +1,82 @@
+/* Naive implementation using a sorted list of pairs [key, [item[1], ..., item[n]]].
+The key may be any number (integer or not). Items are extracted in FIFO order. */
+
+defstruct(pqueue(q = []))$
+
+/* Binary search */
+
+find_key(q, p) := block(
+   [i: 1, j: length(q), k, c],
+   if j = 0 then false
+   elseif (c: q[i][1]) >= p then
+      (if c = p then i else false)
+   elseif (c: q[j][1]) <= p then
+      (if c = p then j else false)
+   else catch(
+      while j >= i do (
+         k: quotient(i + j, 2),
+         if (c: q[k][1]) = p then throw(k)
+         elseif c < p then i: k + 1 else j: k - 1
+      ),
+      false
+   )
+)$
+
+pqueue_push(pq, x, p) := block(
+   [q: pq@q, k],
+   k: find_key(q, p),
+   if integerp(k) then q[k][2]: endcons(x, q[k][2])
+   else pq@q: sort(cons([p, [x]], q)),
+   'done
+)$
+
+pqueue_pop(pq) := block(
+   [q: pq@q, v, x],
+   if emptyp(q) then 'fail else (
+      p: q[1][1],
+      v: q[1][2],
+      x: v[1],
+      if length(v) > 1 then q[1][2]: rest(v) else pq@q: rest(q),
+      x
+   )
+)$
+
+pqueue_print(pq) := block([t], while (t: pqueue_pop(pq)) # 'fail do disp(t))$
+
+
+/* An example */
+
+a: new(pqueue)$
+
+pqueue_push(a, "take milk", 4)$
+pqueue_push(a, "take eggs", 4)$
+pqueue_push(a, "take wheat flour", 4)$
+pqueue_push(a, "take salt", 4)$
+pqueue_push(a, "take oil", 4)$
+pqueue_push(a, "carry out crepe recipe", 5)$
+pqueue_push(a, "savour !", 6)$
+pqueue_push(a, "add strawberry jam", 5 + 1/2)$
+pqueue_push(a, "call friends", 5 + 2/3)$
+pqueue_push(a, "go to the supermarket and buy food", 3)$
+pqueue_push(a, "take a shower", 2)$
+pqueue_push(a, "get dressed", 2)$
+pqueue_push(a, "wake up", 1)$
+pqueue_push(a, "serve cider", 5 + 3/4)$
+pqueue_push(a, "buy also cider", 3)$
+
+pqueue_print(a);
+"wake up"
+"take a shower"
+"get dressed"
+"go to the supermarket and buy food"
+"buy also cider"
+"take milk"
+"take butter"
+"take flour"
+"take salt"
+"take oil"
+"carry out recipe"
+"add strawberry jam"
+"call friends"
+"serve cider"
+"savour !"