Added hard problem

Author: das-jishu

Hard/inverted-bisection.py

@@ -0,0 +1,48 @@
+
+# INVERTED BISECTION
+
+# This is an input class. Do not edit.
+class LinkedList:
+    def __init__(self, value):
+        self.value = value
+        self.next = None
+
+
+def invertedBisection(head):
+    # Write your code here.
+	if head is None or head.next is None:
+		return head
+	
+	prev = None
+    slow = head
+	fast = head
+	while fast and fast.next:
+		prev = slow
+		slow = slow.next
+		fast = fast.next.next
+		
+	hasEvenCount = True if fast == None else False
+	prev.next = None
+	if hasEvenCount:
+		firstHalf = reverseLinkedList(head)
+		secondHalf = reverseLinkedList(slow)
+		head.next = secondHalf
+		return firstHalf
+	else:
+		firstHalf = reverseLinkedList(head)
+		secondHalf = reverseLinkedList(slow.next)
+		head.next = slow
+		slow.next = secondHalf
+		return firstHalf
+
+def reverseLinkedList(head):
+	prev = None
+	cur = head
+	while cur is not None:
+		temp = cur.next
+		cur.next = prev
+		prev = cur
+		cur = temp
+		
+	return prev
+		

Hard/special-strings.py

@@ -0,0 +1,43 @@
+
+# SPECIAL STRINGS
+
+def specialStrings(strings):
+    # Write your code here.
+    trie = Trie()
+	for string in strings:
+		trie.buildTrie(string)
+		
+	specials = []
+	for string in strings:
+		if checkSpecial(string, trie.root, 0, 0, trie):
+			specials.append(string)
+			
+	return specials
+		
+def checkSpecial(string, node, index, count, trie):
+	letter = string[index]
+	if letter not in node:
+		return False
+	
+	if index == len(string) - 1:
+		return trie.endSymbol in node[letter] and count > 0
+	
+	if trie.endSymbol in node[letter]:
+		remainingSpecial = checkSpecial(string, trie.root, index + 1, count + 1, trie)
+		if remainingSpecial:
+			return True
+		
+	return checkSpecial(string, node[letter], index + 1, count, trie)
+
+class Trie:
+	def __init__(self):
+		self.root = {}
+		self.endSymbol = "*"
+		
+	def buildTrie(self, string):
+		current = self.root
+		for letter in string:
+			if letter not in current:
+				current[letter] = {}
+			current = current[letter]
+		current[self.endSymbol] = True