jweinst1
10/19/2016 - 11:49 PM

## more string practice with decoding

more string practice with decoding

``````#String + recursion problems

# "\n" is a newline character. It is not represented visually, but makes a new line

#Staircase is a function that returns a successively indented string with a message repeated in every line, it starts with space x up to space y
"""
print(staircase("TableTennis", 0, 8))
TableTennis
TableTennis
TableTennis
TableTennis
TableTennis
TableTennis
TableTennis
TableTennis
TableTennis
"""
def staircase(message, x, y):
#This creates the spaced string with a certain number of spaces.
# the join method allows you to concat a list fo strings together.
spacer = "".join([" " for i in range(x)])
if x == y:
return spacer + message
else:
return spacer + message + "\n" + staircase(message, x+1, y)

#pyramid is a function similar to staircase but uses recursion to synthesize
#the string in the reverse, descending direction as well
"""
print(pyramid("Berkeley", 8))
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
Berkeley
"""
def pyramid(message, x):
def helper(n):
#way to make a spacer without join method
spacer = ""
for i in range(n):
spacer += " "
if n == x:
return spacer + message
else:
#you need a newline befor and after the recursive call so the descending string has the same indent
return spacer + message + "\n" + helper(n+1) + "\n" + spacer + message
return helper(0)

#The atoi function converts a string to an integer without using the int() function
#This does not work for negative integers
#this function also allows a leading zero
"""
atoi("556")
=> 556
atoi("5566")
=> 5566
atoi("55668888")
=> 55668888
atoi("556068888")
=> 556068888
"""
def atoi(string):
#A dictionary that gets the integer equivalent for one character of a string
digits = {
"0":0,
"1":1,
"2":2,
"3":3,
"4":4,
"5":5,
"6":6,
"7":7,
"8":8,
"9":9
}
if not string[0] in digits:
raise ValueError("Invalid Integer String")
else:
if len(string) == 1:
return digits[string]
else:
#the decimal is the magnitude of the number. This grows exponentially with the length of the string.
decimal = 10 ** (len(string) - 1)
return (digits[string[0]] * decimal) + atoi(string[1:])

#splitstr is a function that splits a string by some occurence of a substr within a string.
#it returns a list of strings without the substr you want to split by
"""
splitstr("abfcdefg", "f")
=> ['ab', 'cde', 'g']
splitstr("how are you today sir", " ")
=> ['how', 'are', 'you', 'today', 'sir']
"""
def splitstr(string, substr):
#the current section of string before a substr occurs
current_split = ""
#the strings that are in fact between occurences of the substr
splits = []
#tells us whether or not we are in the state of checking for a substr
splitmode = False
#keeps track of how far we on checking if a substr has occurred in the string
subindex = 0
for i in range(len(string)):
if splitmode:
#if we have successfully confirmed the occurence of a substr, perform the split
if subindex == len(substr):
#turns off checking for substr
splitmode = False
#append the section fo string before the substr
splits.append(current_split)
#reset the string carrying the string before the substr
current_split = ""
#add the current character to the beginning of the next split
current_split += string[i]
subindex = 0
elif string[i] == substr[subindex]:
subindex += 1
else:
#if the substr is not fully verified via all its characters
splitmode = False
#because this is an improper split, add the previously untracked characters to the main split
current_split += string[i-subindex:i]
subindex = 0
else:
#turn on splitmode if the first char of the substr
#matches the current char of the string
if string[i] == substr[subindex]:
splitmode = True
subindex += 1
else:
current_split += string[i]
splits.append(current_split)
return splits
``````