Duplicated suitors in SuitorGaleShapley algorithm

[Martin Ovesny]

After few iterations the queue of freeSuitors contains duplicit copies of single suiter because they are never excluded from the queue, not even after they get engaged.
This consequently causes NullPointerException (due to the variable w), because even if the prefs are empty the suitor is still in the queue.
Calling freeSuitors.poll(); after each engagement (lines 97 and 104) seems to solve the problem.

[Martin Ovesny]

Snippet:

        // As per wikipedia algorithm
        while (!freeSuitors.isEmpty()) {

            // The next free suitor who has a reviewer to propose to
            MTuple m = freeSuitors.peek();

            // m's highest ranked such woman who he has not proposed to yet
            W w = m.prefs.poll();
            if(w == null) {
                freeSuitors.poll();
                continue;
            }

            // Tf w is free
            if (!engagements.containsKey(w)) {
                // (m, w) become engaged
                engagements.put(w, m);
                freeSuitors.poll();
            } else {
                // Some pair (m', w) already exists
                MTuple mPrime = engagements.get(w);
                if (reviewerPreference(w).compare(mPrime.suitor, m.suitor) < 0) {
                    // (m, w) become engaged
                    engagements.put(w, m);
                    freeSuitors.poll();

                    // m' becomes free
                    freeSuitors.add(mPrime);
                }
            }

        }