First commit

1_2_reverse.py

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+#!/usr/bin/env python
+
+
+def reverse(string):
+    """Reverse a given string."""
+    return string[::-1]
+
+if __name__ == '__main__':
+    print reverse('a')
+    print reverse('abcd')
+    print reverse('hello world')

1_3_duplicate_characters.py

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+#!/usr/bin/env python
+
+
+def remove_duplicates(string):
+    """Remove duplicate characters in a string."""
+    return set(string)
+
+
+def remove_with_dict(string):
+    """Implement my own set function."""
+    string_dict = {}
+    for letter in string:
+        string_dict[letter] = True
+    return string_dict.keys()
+
+if __name__ == '__main__':
+    print remove_duplicates('a')
+    print remove_duplicates('abcd')
+    print remove_duplicates('abcda')
+    print remove_with_dict('a')
+    print remove_with_dict('abcd')
+    print remove_with_dict('abcda')

1_4_anagrams.py

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+#!/usr/bin/env python
+
+
+def anagram(first, second):
+    """Decide if two strings are anagrams of one another."""
+    return sorted(first) == sorted(second)
+
+if __name__ == '__main__':
+    print anagram('a', 'b')
+    print anagram('a', 'A')
+    print anagram('hi', 'hi')
+    print anagram('hello there', 'hello there')

1_5_spaces.py

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+#!/usr/bin/env python
+
+import re
+
+
+def replace_space(string):
+    """Replace all spaces in a word with `%20`."""
+    return re.sub(' ', '%20', string)
+
+if __name__ == '__main__':
+    print replace_space('abcd')
+    print replace_space('hello world')
+    print replace_space('another working example')

1_7_matrix_0.py

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+#!/usr/bin/env python
+
+"""If an element in an MxN matrix is 0, it's row and column are set to 0."""
+
+
+def adjust_matrix(matrix):
+    """
+    Given a matrix of size MxN, if an element is zero, set it's row and
+    column to zeros.
+    """
+    zero_rows = {}
+    zero_columns = {}
+    # Get location of all the zeros.
+    for i, row in enumerate(matrix):
+        for j, num in enumerate(row):
+            if num is 0:
+                zero_rows[i] = True
+                zero_columns[j] = True
+    # Adjust the matrix accordingly.
+    for i, row in enumerate(matrix):
+        for j, num in enumerate(row):
+            # Dictionary lookup is O(1).
+            if i in zero_rows or j in zero_columns:
+                matrix[i][j] = 0
+    return matrix
+
+
+if __name__ == '__main__':
+    matrix = [[1],[2],[3]]
+    print adjust_matrix(matrix)
+
+    matrix = [[1, 2], [1, 0]]
+    print adjust_matrix(matrix)
+
+    matrix = [[1, 2, 3], [1, 2, 0], [1, 2, 3]]
+    print adjust_matrix(matrix)
+
+    matrix = [[1, 2, 3, 4], [1, 2, 3, 4],
+              [1, 2, 0, 4], [1, 2, 3, 4]]
+    print adjust_matrix(matrix)

1_8_substring_rotation.py

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+#!/usr/bin/env python
+
+
+def is_rotation(first, second):
+    """Given two strings, is one a rotation of the other."""
+    if len(first) is not len(second):
+        return False
+    double_second = second + second
+    return first in double_second
+
+if __name__ == '__main__':
+    print is_rotation('apple', 'pleap')  # True
+    print is_rotation('apple', 'ppale')  # False
+    print is_rotation('zach', 'chza')    # True

3_2_stack_with_minimum.py

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+#!/usr/bin/env python
+
+"""
+Design a stack, which in addition to push and pop, also has a function to
+return the minimum element.
+"""
+
+class Stack(list):
+
+    def push(self, number):
+        """Push method -- similar to other languages."""
+        if len(self) > 0:
+            last = self[-1]
+            minimum = self._find_minimum(number, last)
+        else:
+            minimum = number
+        self.minimum = minimum
+        self.append(NodeWithMin(number, minimum))
+
+    def _find_minimum(self, number, last_number):
+        """Internal method to compare two numbers."""
+        if number < last_number.minimum:
+           return number
+        return last_number.minimum
+
+    def min(self):
+        """Return the minimum element."""
+        return self.minimum
+
+
+class NodeWithMin(object):
+
+    def __init__(self, number, minimum):
+        self.number = number
+        self.minimum = minimum
+
+    def __repr__(self):
+        return str(self.number)
+
+    def min(self):
+        return self.minimum
+
+
+def main():
+    z = Stack()
+    z.push(1)
+    z.push(2)
+    z.push(3)
+    node = z.pop()
+    print node.minimum
+    z.push(0)
+    z.push(4)
+    node = z.pop()
+    print node.min()
+    print z.min()
+    print z
+
+if __name__ == '__main__':
+    main()

3_4_hanoi.py

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+#!/usr/bin/env python
+
+"""
+Towers of Hanoi in Python.
+
+Notice how it takes 2^n - 1 number of moves to complete.
+To see this for yourself, run the following from the commandline:
+    python 3_4_hanoi.py | wc -l
+"""
+
+
+def hanoi(n, a='A', b='B', c='C'):
+    """Move n discs from a to c using b as middle."""
+    if n == 0:
+        return
+    hanoi(n-1, a, c, b)
+    print a, '->', c
+    hanoi(n-1, b, a, c)
+
+
+def main():
+    hanoi(4)
+
+if __name__ == '__main__':
+    main()

README.md

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+Cracking the Coding Interview - Python
+======================================
+
+I've been reading the book [Cracking the Coding
+Interview](http://amzn.to/crack_code), and decided to write the answers in
+Python (all of the book's solutions are in Java).