Added #246

Author: subsr97

Diff for: challenges/chain-words.py

@@ -0,0 +1,42 @@
+"""
+#246
+Dropbox
+
+Given a list of words, determine whether the words can be chained to form a circle.
+A word X can be placed in front of another word Y in a circle if the last character of X is same as the first character of Y.
+
+For example, the words ['chair', 'height', 'racket', 'touch', 'tunic'] can form the following circle:
+chair --> racket --> touch --> height --> tunic --> chair.
+
+"""
+
+def checkForCycleHelper(usedWords, remainingWords):
+    if len(remainingWords) == 0:
+        # print(usedWords, end=" ")     # Uncomment to see the chain
+        return True
+    
+    lastLetter = usedWords[-1][-1]
+    for i in range(len(remainingWords)):
+        nextWord = remainingWords[i]
+        if nextWord.startswith(lastLetter) and checkForCycleHelper(usedWords+[nextWord], remainingWords[:i]+remainingWords[i+1:]):
+            return True
+    
+    return False
+
+
+def checkForCycle(words):
+    return checkForCycleHelper([words[0]], words[1:])
+
+def main():
+    print(checkForCycle(["geek", "king"]))                      # True ['geek', 'king']
+    print(checkForCycle(["for", "geek", "rig", "kaf"]))         # True ['for', 'rig', 'geek', 'kaf']
+    print(checkForCycle(["aab", "bac", "aaa", "cda"]))          # True ['aab', 'bac', 'cda', 'aaa']
+    print(checkForCycle(["aaa", "bbb", "baa", "aab"]))          # True ['aaa', 'aab', 'bbb', 'baa']
+    print(checkForCycle(["aaa"]))                               # True ['aaa']
+    print(checkForCycle(["aaa", "bbb"]))                        # False
+    print(checkForCycle(["abc", "efg", "cde", "ghi", "ija"]))   # True ['abc', 'cde', 'efg', 'ghi', 'ija']
+    print(checkForCycle(["ijk", "kji", "abc", "cba"]))          # False
+
+
+if __name__ == "__main__":
+    main()

Diff for: index.md

@@ -55,6 +55,7 @@
 * [#215 Bottom View Of Binary Tree](./challenges/bottom-view-of-binary-tree.py)
 * [#222 Standardize Absolute Path](./challenges/standardize-absolute-path.py)
 * [#244 Sieve Of Eratosthenes - Prime Generator](./challenges/sieve-of-eratosthenes-prime-generator.py)
+* [#246 Chain Words](./challenges/chain-words.py)
 
 ## Lessons