Adrian's CodingBat Exercises Part 2

Screenshots

Warmup 2

warmup2

List 2

list2

String 2

string2

Logic 2

logic2

Exercises

1. String 2: xyz_there

Return True if the given string contains an appearance of "xyz" where the xyz is not directly preceded by a period.

I think I may have made this exercise way more difficult than it was meant to be, but I got to delve into some recursion. At first I tried a for loop and an if statement, similar to the previous string exercises. I got almost all of the tests to work, except for the case where there were two instances of "xyz" with the second one not preceded by a period. I think I understand the solution I came up with, but I couldn't have figured it out without some extensive Internet research.

Code

def xyz_there(str):

  if ("xyz" in str):

    index=str.index("xyz")

    if (index==0):
      return True

    if (not str[index-1] == "."):
      return True

    return xyz_there(str[index+3:])

  return False

2. List 2: sum67

Return the sum of numbers in the array, except ignore sections of numbers starting with a 6 and extending to the next 7.

I had a hard time with the last three list problems, but I decided to highlight this one because I used a while loop and the delete method for the first time. At one point I was got a "Timed Out" error and I'm not sure why. I also got the error during a few other exercises when I attempted a while loop.

Code

def sum67(nums):
  while (6 in nums)
    i = nums.index(6)
    j = nums.index(7, i, len(nums))
    del nums[i:j+1]
  return sum(nums)

3. Logic 2: lone_sum

Given 3 int values, a b c, return their sum. However, if one of the values is the same as another of the values, it does not count towards the sum.

There were a few logic exercises that took me more time to figure out, but one thing I want to learn more of is how to write more condensed, elegant code. I'm sure there is a better way to do this than the way I did.

Code

def lone_sum(a, b, c):
  if a==b and a==c:
    return 0
  if a==b:
    return c
  if a==c:
    return b
  if b==c:
    return a
  return a+b+c

SILShack Spring 2014