[Feature] Two methods of finding the longest common prefix in a list of words!

Author: exterkamp

README.md

@@ -62,4 +62,7 @@ Different algorithmic programs.  Grouped by general topic.
 * [Permutations](algorithms/string/permutations.py)
 * [Combinations](algorithms/string/combinations.py)
   * [Letters in Word](algorithms/string/combinations.py)
-  * [Letters from Phone](algorithms/string/combinations.py)
+  * [Letters from Phone](algorithms/string/combinations.py)
+* [Longest Common Prefix](algorithms/string/longest_common_prefix.py)
+  * [Trie](algorithms/string/longest_common_prefix.py)
+  * [Reduce](algorithms/string/longest_common_prefix.py)

algorithms/string/longest_common_prefix.py

@@ -0,0 +1,37 @@
+from functools import reduce
+from structures.trie import Trie
+
+def find_longest_common_prefix(words:list):
+    """
+    Find the longest common prefix in a list of words.
+
+    """
+    trie = Trie(words)
+
+    head = trie.head
+
+    prefix = []
+
+    while len(head) == 1 and trie.eof not in head:
+        key, value = head.popitem()
+        prefix.append(key)
+        head = value
+    
+    return "".join(prefix)
+
+def find_longest_common_prefix_reduce(words:list):
+    """
+    Find the lcp in a list of words, using 'reduce' functions.
+
+    """
+    if not words:
+        return ''
+    
+    def common_start(w1, w2):
+        shorter = w1 if len(w1) < len(w2) else w2
+        for i in range(0, len(shorter)):
+            if w1[i] != w2[i]:
+                return shorter[:i]
+        return shorter
+    
+    return reduce(common_start, words)

structures/graph.py

@@ -8,4 +8,11 @@ def add_adjacent(self, node):
         self.adjacent_list.add(node)
 
     def remove_adjacent(self, node):
-        self.adjacent_list.remove(node)     
+        self.adjacent_list.remove(node)
+    
+    def contains_universal_sink(self):
+        """
+        Check if this node is part of a graph with a universal sink.
+
+        """
+        

tests/test_longest_common_prefix.py

@@ -0,0 +1,20 @@
+import unittest
+from algorithms.string.longest_common_prefix import find_longest_common_prefix, find_longest_common_prefix_reduce
+
+class TestLongestCommonPrefix(unittest.TestCase):
+
+    def test_lcp(self):
+        self.assertEqual('he', find_longest_common_prefix(['hello','hellieo','he']))
+        self.assertEqual('he', find_longest_common_prefix_reduce(['hello','hellieo','he']))
+    
+    def test_lcp_empty(self):
+        self.assertEqual('', find_longest_common_prefix([]))
+        self.assertEqual('', find_longest_common_prefix_reduce([]))
+    
+    def test_lcp_no_prefix(self):
+        self.assertEqual('', find_longest_common_prefix(['fcp','jpl','the','first']))
+        self.assertEqual('', find_longest_common_prefix_reduce(['fcp','jpl','the','first']))
+    
+    def test_lcp_full_prefix(self):
+        self.assertEqual('full', find_longest_common_prefix(['full','full','full']))
+        self.assertEqual('full', find_longest_common_prefix_reduce(['full','full','full']))