In this post, we have provided solutions to python Problem Set 1 of Introduction to Computer Science & Programming Using Python of Edx Course.

Note: Use the solution for your reference only. During the final submission, please use your own code. Thank You 🙂

## Introduction to Computer Science & Programming Using Python Problem Set 1:

### Problem 1 Description:

Assume `s` is a string of lower case characters.

Write a program that counts up the number of vowels contained in the string `s`. Valid vowels are: ‘`a`‘, ‘`e`‘, ‘`i`‘, ‘`o`‘, and ‘`u`‘. For example, if `s = 'azcbobobegghakl'`, your program should print:

`Number of vowels: 5`

### The solution to Problem 1:

count = 0
vowels = [‘a’ , ‘e’ , ‘i’ ,’o’ , ‘u’]
for char in s:
if char in vowels:
count += 1
print (‘Number of vowels: ‘ + str(count))

### Problem 2 Description:

Assume `s` is a string of lower case characters.

Write a program that prints the number of times the string `'bob'` occurs in `s`. For example, if `s = 'azcbobobegghakl'`, then your program should print

`Number of times bob occurs is: 2`

### Problem 2 Solution:

Count = 0
for i in range(len(s)):
if (s[i:i+3] == “bob”):
Count = Count + 1

print(“Number of times bob occurs is: ” + str(Count))

### Problem 3 Description:

Assume `s` is a string of lower case characters.

Write a program that prints the longest substring of `s` in which the letters occur in alphabetical order. For example, if `s = 'azcbobobegghakl'`, then your program should print

`Longest substring in alphabetical order is: beggh`

In the case of ties, print the first substring. For example, if `s = 'abcbcd'`, then your program should print

`Longest substring in alphabetical order is: abc`

Note: This problem may be challenging. We encourage you to work smart. If you’ve spent more than a few hours on this problem, we suggest that you move on to a different part of the course. If you have time, come back to this problem after you’ve had a break and cleared your head.

### Problem 3 Solution:

first=0
second=1
strang1=”
strang2=”
while second<len(s):
if second>=len(s):
break
elif s[first]<=s[second]:
strang1+=s[first:second+1]
while second<=len(s):
second+=1
if second>=len(s):
break
elif s[second]>=strang1[-1]:
strang1+=s[second]
if len(strang1)>len(strang2):
strang2=strang1
else:
if len(strang1)>len(strang2):
strang2=strang1
strang1=”
first=second-1
break
else:
if len(s[first])>len(strang2):
strang2=s[first]
first+=1
second+=1
print(“Longest substring in alphabetical order is:” + strang2)

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