#!/usr/bin/env python
# coding: utf-8

# This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

# # Challenge Notebook

# ## Problem: Find the magic index in an array, where array[i] = i.
# 
# * [Constraints](#Constraints)
# * [Test Cases](#Test-Cases)
# * [Algorithm](#Algorithm)
# * [Code](#Code)
# * [Unit Test](#Unit-Test)
# * [Solution Notebook](#Solution-Notebook)

# ## Constraints
# 
# * Is the array sorted?
#     * Yes
# * Are the elements in the array distinct?
#     * No
# * Does a magic index always exist?
#     * No
# * If there is no magic index, do we just return -1?
#     * Yes
# * Are negative values allowed in the array?
#     * Yes
# * If there are multiple magic values, what do we return?
#     * Return the left-most one
# * Can we assume this fits memory?
#     * Yes

# ## Test Cases
# 
# * None input -> -1
# * Empty array -> -1
# 
# <pre>
# a[i]  -4 -2  2  6  6  6  6 10
#   i    0  1  2  3  4  5  6  7
# </pre>
# 
# Result: 2
# 
# <pre>
# a[i]  -4 -2  1  6  6  6  6 10
#   i    0  1  2  3  4  5  6  7
# </pre>
# 
# Result: 6
# 
# <pre>
# a[i]  -4 -2  1  6  6  6  7 10
#   i    0  1  2  3  4  5  6  7
# </pre>
# 
# Result: -1

# ## Algorithm
# 
# Refer to the [Solution Notebook]().  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

# ## Code

# In[ ]:


class MagicIndex(object):

    def find_magic_index(self, array):
        # TODO: Implement me
        pass


# ## Unit Test

# **The following unit test is expected to fail until you solve the challenge.**

# In[ ]:


# %load test_find_magic_index.py
import unittest


class TestFindMagicIndex(unittest.TestCase):

    def test_find_magic_index(self):
        magic_index = MagicIndex()
        self.assertEqual(magic_index.find_magic_index(None), -1)
        self.assertEqual(magic_index.find_magic_index([]), -1)
        array = [-4, -2, 2, 6, 6, 6, 6, 10]
        self.assertEqual(magic_index.find_magic_index(array), 2)
        array = [-4, -2, 1, 6, 6, 6, 6, 10]
        self.assertEqual(magic_index.find_magic_index(array), 6)
        array = [-4, -2, 1, 6, 6, 6, 7, 10]
        self.assertEqual(magic_index.find_magic_index(array), -1)
        print('Success: test_find_magic')


def main():
    test = TestFindMagicIndex()
    test.test_find_magic_index()


if __name__ == '__main__':
    main()


# ## Solution Notebook
# 
# Review the [Solution Notebook]() for a discussion on algorithms and code solutions.