add boilerplate for second edition

first_edition/ebook_src/trees/trie.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+'''
+Implement a trie. (Write the API and code for inserting into a trie).
+'''
+
+def make_trie(*args):
+    trie = {}
+
+    for word in args:
+        temp_trie = trie
+        for letter in word:
+            temp_trie = temp_trie.setdefault(letter, {})
+        temp_trie = temp_trie.setdefault('_end_', '_end_')
+
+    return trie
+
+
+def in_trie(trie, word):
+    temp_trie = trie
+    for letter in word:
+        if letter not in temp_trie:
+            return False
+        temp_trie = temp_trie[letter]
+    return True
+
+
+def remove_from_trie(trie, word, depth):
+    if word and word[depth] not in trie:
+        return False
+
+    if len(word) == depth + 1:
+        del trie[word[depth]]
+        if not trie:
+           return True
+        return False
+    else:
+        temp_trie = trie
+
+        if remove_from_trie(temp_trie[word[depth]], word, depth + 1):
+            if temp_trie:
+                del temp_trie[word[depth]]
+            return not temp_trie
+    return False
+
+
+if __name__ == '__main__':
+    trie = make_trie('hello', 'abc', 'baz', 'bar', 'barz')
+    print 'This is the trie:'
+    print trie
+
+    assert(in_trie(trie, 'hello') == True)
+    assert(in_trie(trie, 'bar') == True)
+    assert(in_trie(trie, 'bab') == False)
+    assert(in_trie(trie, 'zzz') == False)
+
+    remove_from_trie(trie, 'abc', 0)
+    assert(in_trie(trie, 'abc') == False)
+
+
+
+