first commit: code for chapter 1

01_introduction_to_algorithms/python/01_binary_search.py

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+def binary_search(list, item):
+  # low and high keep track of which part of the list you'll search in.
+  low = 0
+  high = len(list) - 1
+
+  # While you haven't narrowed it down to one element ...
+  while low <= high:
+    # ... check the middle element
+    mid = (low + high) // 2
+    guess = list[mid]
+    # Found the item.
+    if guess == item:
+      return mid
+    # The guess was too high.
+    if guess > item:
+      high = mid - 1
+    # The guess was too low.
+    else:
+      low = mid + 1
+
+  # Item doesn't exist
+  return None
+
+my_list = [1, 3, 5, 7, 9]
+print binary_search(my_list, 3) # => 1
+
+# 'None' means nil in Python. We use to indicate that the item wasn't found.
+print binary_search(my_list, -1) # => None