Merge pull request #9 from destag/add-elo

Add elo rating calculation (#2)

python-exercises/elo.py

@@ -0,0 +1,20 @@
+def elo(player_rating, opponent_rating, won, k=32):
+    q1 = 10**(player_rating / 400)
+    q2 = 10**(opponent_rating / 400)
+
+    expected_score = q1 / (q1 + q2)
+    true_score = int(won)
+
+    final_score = player_rating + k * (true_score - expected_score)
+    return int(final_score)
+
+
+rating1 = int(input('First player score: '))
+rating2 = int(input('Second player score: '))
+player1_won = int(input('Which player won? [1/2]: ')) == 1
+
+new_rating1 = elo(rating1, rating2, player1_won)
+new_rating2 = elo(rating2, rating1, not player1_won)
+
+print('Player 1 new score: {}. Change: {}'.format(new_rating1, new_rating1 - rating1))
+print('Player 2 new score: {}. Change: {}'.format(new_rating2, new_rating2 - rating2))