Adrian's CodingBat Exercises Part 1

Screenshots

Warmup 1

warmup1

List 1

list1

String 1

string1

Logic 1

logic1

Exercises

1. String 1: extra_end

Given a string, return a new string made of 3 copies of the last 2 chars of the original string. The string length will be at least 2.

I had the same problem with several of the string exercises, where I incorrectly guessed the numbers that I needed to use in the index operator to grab certain parts of a string. For this one, I started with str[-2:-1] but it only retrieved the second-to-last letter.

Code

def extra_end(str):
  newstr = str[-2:]*3
  return newstr

2. List 1: rotate_left3

Given an array of ints length 3, return an array with the elements "rotated left" so {1, 2, 3} yields {2, 3, 1}.

At first glance, I didn't think this exercise would give me any trouble, but I could not figure it out on my own! So after some Googling, I found out about the pop method which removes and returns an arbitrary element from a set. After some trial-and-error I combined the append and pop methods to rotate the list.

Code

def rotate_left3(nums):
   nums.append(nums.pop(0))
   return nums

3. Warmup 1: post_neg

Given 2 int values, return True if one is negative and one is positive. Except if the parameter "negative" is True, then return True only if both are negative.

I learned a lot from this one about how to condense my code. You can see my code first followed by CodingBat's solution, which is a lot more "Pythonic" and showed me that you don't have to explicitly return True or False.

Code

def pos_neg(a, b, negative):
  if negative and (b < 0 and a < 0):
    return True
  if negative and a > 0 and b < 0:
    return False
  if not negative and a < 0 and b > 0 or a > 0 and b < 0:
    return True
  else:
    return False

CodingBat's Solution

def pos_neg(a, b, negative):  
  if negative:    
    return (a < 0 and b < 0)  
  else: 
    return ((a < 0 and b > 0) or (a > 0 and b < 0))

SILShack Spring 2014