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week-3-messy-medians.clj
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week-3-messy-medians.clj
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; Week 3
(require '[clojure.string :as str])
(def lines-vector
[1 5 -2 3 2 5 4 -7 2 -3])
(defn median [vector]
(let [sorted (vec (sort (filter pos? vector)))
vec-length (count vector)
middle-index (if (odd? vec-length)
(- (Math/round (/ vec-length 2.0)) 1)
(- (/ vec-length 2) 1))]
(get sorted middle-index)))
; Algorithm:
;
; Things to keep track of: states, the next lines, and the current iteration
; States are the values we're calculating the median with
; states: { 1 => [1], 2 => [1 5] } etc.
; Base case: if there are no more lines to read, return
; Recursive case:
; - set previous state to the state during the last iteration, or an empty
; vector if there was none
; if we're rolling back (the current line is a negative num)
; - calculate the state we want to rollback to and fetch it from the states map/dictionary
; - set the state for this iteration to the rolled-back state
; - print the median of this current state
; - recurse w/ new values
; if we're not rolling back,
; - add the current number to the previous set of numbers
; - calculate the median of that
; - recurse w/ new values
(defn messy-median [states, lines, iteration]
(if (empty? lines)
nil
(let [previous-state (if (empty? states) [] (states (- iteration 1)))
current-line (first lines)
new-lines (rest lines)]
(if (> 0 current-line)
(let [rollback-to (+ iteration current-line)
current-state (states rollback-to)
new-states (assoc states iteration current-state)]
(println (median current-state))
(messy-median new-states new-lines (+ 1 iteration)))
(let [current-state (conj previous-state current-line)
new-states (assoc states iteration current-state)]
(println (median current-state))
(messy-median new-states new-lines (+ 1 iteration)))))))
(messy-median {} lines-vector 0)