Mostly works

bottlenecks.clj

(ns ieee2013.carpalind)

(require 'clojure.set)

(defn read-in [] 
  (let [n (- (read-string (read-line)) 1)]
    (clojure.string/trim 
     (apply str (for [x (range n)]
                  (str (read-line) " "))))))

(defn find-bottlenecks []
  (let [input (read-in)
        parsed-input (map keyword (clojure.string/split input #"\s+"))
        vertices (set parsed-input)
        edges (apply merge-with clojure.set/union (map #(hash-map (first %) #{(second %)}) (partition 2 parsed-input)))
        pruned (clojure.set/difference vertices (apply clojure.set/union (vals edges)))]
    (loop [k pruned
           res []]
      (let [next-keys (apply clojure.set/union (vals (select-keys edges k)))]
        (if (seq next-keys)
          (recur next-keys
                 (conj res k))
          (conj res next-keys))))))

(doall (map (comp println name) 
            (reduce into (sorted-set) 
                    (filter #(= (count %1) 1) 
                            (find-bottlenecks)))))