Exercise $1$

Assume s is a string of characters. Write a program that counts the number of vowels contained in the string s$.$ Valid vowels are both lower$-$ and uppercase: $\text{'}$a$\text{'},\text{'}$e$\text{'},\text{'}$i$\text{'},\text{'}$o$\text{'},\text{'}$u$\text{'},\text{'}$A$\text{'},\text{'}$E$\text{'},\text{'}$I$\text{'},\text{'}$O$\text{'},$ and $\text{'}$U$\text{'}.$

For example, if s $=$ 'azcbobobegghAkl', your program should return $5.$

# GRADED CELL: def countVowels$($s$)$: # Counts the number of vowels # input: string s of characters # output: number of vowels in s counter$=0$ # counts the number of vowels ### START CODE HERE ### ### END CODE HERE ### return counter

# Quick Check s$1=$'azcbobobegghAkl' s$2=$'mdorJKLbnajwyrh$346$$#$\%$&aao$7$me$\text{'}$ s$3=$'hdgftygvetYqnjsvPOIciokjyly$23$MYOAsvx' t$1=$ countVowels$($s$1)$ t$2=$ countVowels$($s$2)$ t$3=$ countVowels$($s$3)$ print$(\text{'}$Output:$\text{'},$t$1,\text{'},\text{'},$t$2,\text{'},\text{'},$t$3)$ print$(\text{'}$Expected output: $5,6,7\text{'})$ if $($t$1,$t$2,$t$3)==(5,6,7)$: print$("$Congratulations$,$ all tests passed successfully!"$)$ else: print$("$Sorry$,$ try again!"$)$

Exercise $2$

Assume s is a string of characters. Write a program that outputs the number of times the string 'bob' in any combination of upper$-$ and lowercase letters $($i$.$e$.,$ 'bob', 'boB', 'bOb', 'bOB', 'Bob', 'BoB', 'BOb',and 'BOB'$)$ occurs in s$.$

# GRADED CELL: def countBob$($s$)$: # Counts the number of times 'bob' appears in s # input: string s # output: number of times 'bob' appears in s counter$=0$ # counts the number of vowels ### START CODE HERE ### ### END CODE HERE ### return counter

# Quick Check s$1=$'azcbobobegghakl' s$2=$'mBOBOBOBmnddbvbobnshbohetg' s$3=$'bobmnfghbobOBbeyhrb$2874$bnbobob' t$1=$ countBob$($s$1)$ t$2=$ countBob$($s$2)$ t$3=$ countBob$($s$3)$ print$(\text{'}$Output:$\text{'},$t$1,\text{'},\text{'},$t$2,\text{'},\text{'},$t$3)$ print$(\text{'}$Expected output: $2,4,5\text{'})$ if $($t$1,$t$2,$t$3)==(2,4,5)$: print$("$Congratulations$,$ all tests passed successfully!"$)$ else: print$("$Sorry$,$ try again!"$)$

Exercise $3$

Assume s is a string of lowercase letters. Write a program that outputs the longest substring of s in which the letters occur in alphabetical order. If two or more such substrings are possible, return the most left one.

Example: s $=$ 'abbampfxxaaa'. There are four longest substrings of s of length $3$: 'abb', 'amp', $\text{'}$fxx$\text{'}$ and 'aaa'. Your code should return 'abb'.

Note: Lowercase letters are alphabetically ordered in Python, i$.$e$.$ a $<$ b$<$ c $<...<$ z$.$

# GRADED CELL: def longestAlphSubStr$($s$)$: # Returns the longest substring of s which is the in alphabetical order # input: string s composed of lowercase letters # output: longest substring of s which is the in alphabetical order longest $=$ s$[0]$ # stores the longest substring of s which is the in alphabetical order ### START CODE HERE ### ### END CODE HERE ### return longest

# Quick Check s$1=$'azcbobobegghakl' s$2=$'abbampfxxaaa' s$3=$'bobmnfghbobbeqqrtxzyhrbbnbobob' t$1=$ longestAlphSubStr$($s$1)$ t$2=$ longestAlphSubStr$($s$2)$ t$3=$ longestAlphSubStr$($s$3)$ print$(\text{'}$Output:$\text{'},$ t$1,\text{'},\text{'},$t$2,\text{'},\text{'},$t$3)$ print$(\text{'}$Expected output: $\text{'}+$'beggh, $\text{'}+$'abb, $\text{'}+$'bbeqqrtxz'$)$ if $($t$1,$t$2,$t$3)==(\text{'}$beggh$\text{'},$'abb','bbeqqrtxz'$)$: print$("$Congratulations$,$ all tests passed successfully!"$)$ else: print$("$Sorry$,$ try again!"$)$