added Favorite Genres

Author: minhyeong-joe

Others/FavoriteGenres/README.md

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+# Favorite Genres
+
+[Leetcode Link](https://leetcode.com/discuss/interview-question/373006)
+
+## Problem:
+
+Given a map `Map<String, List<String>>` userSongs with user names as keys and a list of all the songs that the user has listened to as values.
+
+Also given a map `Map<String, List<String>>` songGenres, with song genre as keys and a list of all the songs within that genre as values. The song can only belong to only one genre.
+
+The task is to return a map `Map<String, List<String>>`, where the key is a user name and the value is a list of the user's favorite genre(s). Favorite genre is the most listened to genre. A user can have more than one favorite genre if he/she has listened to the same number of songs per each of the genres.
+
+## Example:
+
+```
+Input:
+userSongs = {
+   "David": ["song1", "song2", "song3", "song4", "song8"],
+   "Emma":  ["song5", "song6", "song7"]
+},
+songGenres = {
+   "Rock":    ["song1", "song3"],
+   "Dubstep": ["song7"],
+   "Techno":  ["song2", "song4"],
+   "Pop":     ["song5", "song6"],
+   "Jazz":    ["song8", "song9"]
+}
+
+Output: {
+   "David": ["Rock", "Techno"],
+   "Emma":  ["Pop"]
+}
+
+Explanation:
+David has 2 Rock, 2 Techno and 1 Jazz song. So he has 2 favorite genres.
+Emma has 2 Pop and 1 Dubstep song. Pop is Emma's favorite genre.
+```
+
+```
+Input:
+userSongs = {
+   "David": ["song1", "song2"],
+   "Emma":  ["song3", "song4"]
+},
+songGenres = {}
+
+Output: {
+   "David": [],
+   "Emma":  []
+}
+```

Others/FavoriteGenres/solution.py

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+from collections import defaultdict, Counter
+
+
+def favoriteGenres(userSongs, songGenres):
+    result = defaultdict(list)
+    songGenreMap = dict()
+    # create a map 1-to-1 map from song to genre
+    for genre, songs in songGenres.items():
+        for song in songs:
+            songGenreMap[song] = genre
+    # print(songGenreMap)
+    # init result dict with names and genres
+    for user, songs in userSongs.items():
+        for song in songs:
+            if song in songGenreMap:
+                result[user].append(songGenreMap[song])
+    # print(result)
+    # keep the most genres
+    for user, genres in result.items():
+        counter = Counter(genres)
+        maxCount = max(counter.values())
+        result[user] = [genre for genre in counter if counter[genre] == maxCount]
+    # print(result)
+    return result
+
+
+userSongs = {
+    "David": ["song1", "song2", "song3", "song4", "song8"],
+    "Emma":  ["song5", "song6", "song7"]
+}
+songGenres = {
+    "Rock":    ["song1", "song3"],
+    "Dubstep": ["song7"],
+    "Techno":  ["song2", "song4"],
+    "Pop":     ["song5", "song6"],
+    "Jazz":    ["song8", "song9"]
+}
+print(favoriteGenres(userSongs, songGenres))
+userSongs = {
+    "David": ["song1", "song2"],
+    "Emma":  ["song3", "song4"]
+}
+songGenres = {}
+
+print(favoriteGenres(userSongs, songGenres))