path: root/basic_python/practice_ds.tex

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% Tutorial slides on Python.
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% Author: FOSSEE
% Copyright (c) 2017, FOSSEE, IIT Bombay
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\documentclass[14pt,compress]{beamer}

\input{macros.tex}

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% Title page
\title[Basic Python]{Practice exercises: data structures}

\author[FOSSEE Team] {The FOSSEE Group}

\institute[FOSSEE -- IITB] {Department of Aerospace Engineering\\IIT Bombay}
\date[] {Mumbai, India}
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% DOCUMENT STARTS
\begin{document}

\begin{frame}
  \titlepage
\end{frame}

\begin{frame}[fragile,plain]
  \frametitle{Note: Python 2.x and 3.x}

 If you are using Python 2.x
  \begin{itemize}
  \item Use \typ{raw\_input} instead of \typ{input}
  \item Use the following for \typ{print}
  \end{itemize}
 \begin{lstlisting}
from __future__ import print_function
\end{lstlisting}
\end{frame}

\begin{frame}[plain]
  \frametitle{Exercise: simple list creation}
  \begin{enumerate}
  \item Ask the user to enter an integer, \typ{n}
  \item Create a list of integers from 0 to \typ{n-1}
  \item Print this list
  \end{enumerate}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  n = int(input())
  x = list(range(n))
  print(x)
\end{lstlisting}
\end{frame}

\begin{frame}[plain]
  \frametitle{Exercise: more list creation}
  \begin{enumerate}
  \item Ask the user to enter an integer, \typ{n}
  \item Store the square of all the odd numbers less than \typ{n} in a list
  \item Print this list
  \end{enumerate}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  n = int(input())
  result = []
  for i in range(1, n, 2):
      result.append(i*i)
  print(result)
\end{lstlisting}
\end{frame}

\begin{frame}[plain]
  \frametitle{Exercise: tuple creation}
  \begin{enumerate}
  \item Ask the user to enter an integer, \typ{n}
  \item Store the square of all the odd numbers less than \typ{n}
  \item Print a tuple of this list
  \end{enumerate}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  n = int(input())
  result = []
  for i in range(1, n, 2):
      result.append(i*i)
  print(tuple(result))
\end{lstlisting}
\end{frame}


\begin{frame}[plain,fragile]
  \frametitle{Hint: string to list/tuple}
  Here is an easy way to convert a string to a list of characters.

  Try this:
  \begin{lstlisting}
    In []: x = 'hello'
    In []: print(list(x))
    In []: print(tuple(x))
  \end{lstlisting}
\end{frame}

\begin{frame}[plain]
  \frametitle{Exercise: list of Fibonacci}
  \begin{enumerate}
  \item Ask the user to enter an integer, \typ{n} ($\geq 1$)
  \item Store the first \typ{n} numbers of the Fibonnaci series in a list
  \item Print this list
  \end{enumerate}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  n = int(input())
  a, b = 0, 1
  result = [0]
  for i in range(n-1):
      result.append(b)
      a, b = b, a+b
  print(result)
\end{lstlisting}
\end{frame}

\begin{frame}[plain,fragile]
  \frametitle{Exercise: square a list of integers}
  \begin{enumerate}
  \item Ask the user to enter a list of integers separated by spaces
  \item Convert this into a list of integers but square each element
  \item Print this list
  \end{enumerate}
  For example, if the user enters \typ{1 2 3 4}, print:
  \begin{lstlisting}
    [1, 4, 9, 16]
  \end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  text = input()
  result = []
  for item in text.split():
      x = int(item)
      result.append(x*x)
  print(result)
\end{lstlisting}
\end{frame}

\begin{frame}[plain,fragile]
  \frametitle{Exercise: list of tuples}
  \begin{enumerate}
  \item Ask the user to enter a list of integers separated by spaces
  \item Convert this into a list of integers but square each element
  \item Store the integer and its square in a tuple, put this into a list
  \item Print this list
  \end{enumerate}
  For example, if the user enters \typ{1 2 3 4}, print:
  \begin{lstlisting}
    [(1, 1), (2, 4), (3, 9), (4, 16)]
  \end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  text = input()
  result = []
  for item in text.split():
      x = int(item)
      result.append((x, x*x))
  print(result)
\end{lstlisting}
\end{frame}

\begin{frame}[plain,fragile]
  \frametitle{Hint: iterating over a list of tuples}
  Consider the following code:
  \begin{small}
  \begin{lstlisting}
In []: data = [(1, 1), (2, 4), (3, 9), (4, 16)]
\end{lstlisting}
\end{small}
We can iterate over this as follows:
\begin{small}
\begin{lstlisting}
In []: for x, y in data:
.....:     print(x, y)
\end{lstlisting}
\end{small}
\end{frame}


\begin{frame}[plain,fragile]
  \frametitle{Exercise: list methods}
  \begin{enumerate}
  \item Ask the user to enter a string
  \item Convert this into a list of characters
  \item Sort this list in ascending order
  \item Now eliminate any repeated values in this list
  \item Print this list
  \end{enumerate}
  For example, if the user enters \typ{hello}, print:
  \begin{lstlisting}
    ['e', 'h', 'l', 'o']
  \end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  text = input()
  chars = list(text)
  chars.sort()
  result = []
  for c in chars:
      if c not in result:
          result.append(c)
  print(result)
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Another solution}
\begin{lstlisting}
  text = input()
  chars = set(text)
  chars = list(chars)
  chars.sort()
  print(chars)
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Another solution}
\begin{lstlisting}
  chars = set(input())
  print(sorted(chars))
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain,fragile]
  \frametitle{Exercise: simple dictionaries}
  \begin{enumerate}
  \item Ask the user for a list of integers separated by spaces
  \item For each integer, store the string version as the key and the square of
    the integer value as the value in a dictionary.
  \item Print the resulting dictionary
  \end{enumerate}
For example if the user enters "1 3 5", print:
\begin{lstlisting}
{'1': 1, '3': 9, '5': 25}
\end{lstlisting}
Hint: simply print the resulting dictionary
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
text = input()
d = {}
for item in text.split():
    x = int(item)
    d[item] = x*x
print(d)
\end{lstlisting}
\end{frame}


\begin{frame}[fragile,plain,fragile]
  \frametitle{Exercise: mapping using dicts}
  \begin{enumerate}
  \item Create a mapping from 3 character month name to month number
  \item Hint: for example \typ{\{'jan': 1, 'dec': 12\}}
  \item Ask the user for a 3 character month code lower/upper mixed
  \item Print the month number corresponding to the month the user entered.
  \end{enumerate}
For example if the user enters "Jul", print:
\begin{lstlisting}
7
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
months = ('jan feb mar apr may jun jul ' +
         'aug sep oct nov dec').split()
month2mm = {}
for i in range(len(months)):
    month2mm[months[i]] = i + 1

text = input()
mon = text[:3].lower()
print(month2mm[mon])
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Aside: using \typ{enumerate} example}
\begin{lstlisting}
for i, char in enumerate('hello'):
    print(i, char)
\end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Aside: using \typ{enumerate}}
\begin{lstlisting}
months = ('jan feb mar apr may jun jul ' +
         'aug sep oct nov dec').split()
month2mm = {}
for i, month in enumerate(months):
    month2mm[month] = i + 1

# Is easier/nicer than this:

for i in range(len(months)):
    month2mm[months[i]] = i + 1
\end{lstlisting}

\end{frame}



\begin{frame}[plain,fragile]
  \frametitle{Exercise: dictionaries}
  \begin{enumerate}
  \item Ask the user to enter a string
  \item Convert this to lower case
  \item Count the number of occurrences of each character in the string
  \item Hint: use a dict
  \item Print the result in sorted order of the characters
  \end{enumerate}
  For example, if the user enters \typ{helloo}, print:
  \begin{lstlisting}
    e 1
    h 1
    l 2
    o 2
  \end{lstlisting}
\end{frame}

\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
  text = input().lower()
  result = {}
  for char in text:
      if char in result:
          result[char] += 1
      else:
          result[char] = 1

  for char in sorted(result):
      print(char, result[char])
\end{lstlisting}
\end{frame}


\begin{frame}[plain]
  {Problem: datestring to date tuple}

  You are given date strings of the form ``29 Jul, 2009'', or ``4 January
  2008''. In other words a number, a string and another number, with a comma
  sometimes separating the items.

  Write a program that takes such a string as input and prints a tuple (yyyy,
  mm, dd) where all three elements are ints.
\end{frame}

\begin{frame}[fragile]
  \frametitle{Solution}
 \small
  \begin{lstlisting}
months = ('jan feb mar apr may jun jul ' +
         'aug sep oct nov dec').split()
month2mm = {}
for i, month in enumerate(months):
    month2mm[month] = i + 1

date = input()
date = date.replace(',', ' ')
day, month, year = date.split()

dd, yyyy = int(day), int(year)
mon = month[:3].lower()
mm = month2mm[mon]
print((yyyy, mm, dd))
\end{lstlisting}
\end{frame}

\begin{frame}
  \centering
  \Huge

  That's all folks!
\end{frame}
\end{document}