Create 819-most_common_word.py

Author: stevestar888

819-most_common_word.py

@@ -0,0 +1,41 @@
+"""
+https://leetcode.com/problems/most-common-word/
+
+Strat:
+    This is what the solution calls a "pipeline" lol. Essentially taking the 
+    problem into steps: preprocess the punctuations and spaces, and then use 
+    a dictionary to store the occurence of each word.
+    
+Stats: O(n + m) time, O(n + m) space where n is len(paragraph), m is len(banned)
+        ^ have to iterate through both arrays, and both use a set or dict
+    Runtime: 12 ms, faster than 99.75% of Python online submissions for Most Common Word.
+    Memory Usage: 12.7 MB, less than 58.35% of Python online submissions for Most Common Word.
+
+"""
+class Solution(object):
+    def mostCommonWord(self, paragraph, banned):
+        """
+        :type paragraph: str
+        :type banned: List[str]
+        :rtype: str
+        """
+        #bring to lowercase
+        paragraph = paragraph.lower()
+        
+        #preprocess to get rid of punctuation symbols (!?',;.)
+        symbols = "!?',;."
+        for symbol in symbols:
+            paragraph = paragraph.replace(symbol, " ")
+        
+        banned_words = set(banned)
+        
+        counts = {}
+        words = paragraph.split()
+        for word in words:
+            if word not in banned_words:
+                counts[word] = counts.get(word, 0) + 1
+        
+        ##using max instead of sort reduces runtime from nlgn to n
+        # return sorted(counts.items(), key=lambda x: x[1], reverse=True)[0][0]
+        max_pair = max(counts.items(), key=lambda x: x[1])
+        return max_pair[0]