clean up repo.

add more notes

chapter4/README.md

@@ -0,0 +1,12 @@
+# Recursion
+
+Recursive functions must have both:
+
+-   one or more base cases
+-   a recursive case
+
+The base cases are required to ensure the recursion stops when meeting a condition
+
+The recursive case adds functions onto the call stack and completes each one top down.
+
+Note. Quicksort should be implemented using a random pivot to ensure average runtimes.

chapter4/binary.py

@@ -32,10 +32,14 @@ SAMPLE_SIZE = 1000
 numbers = random.sample(range(LOWER, UPPER), SAMPLE_SIZE)
 numbers.sort()
 
+seen = set()
+count = 0
 result = None
 while result is None:
     guess = random.randrange(LOWER, UPPER)
-    logger.debug(f"guess: {guess}")
-    result = binary_search(numbers, 0, len(numbers) - 1, guess)
+    if guess not in seen:
+        count += 1
+        seen.add(guess)
+        result = binary_search(numbers, 0, len(numbers) - 1, guess)
 
-print(f"Found {guess} at index {result}.")
+print(f"Found {guess} at index {result} after {count} attempts.")