Page 364 - Computer Science V2.0 Class 11

● On execution of lines 10–12, for every character in the string, if the character is not included (not present) in the
string distinctChars, it is concatenated to distinctChars.
● On execution of line 13, finally, the function returns a string (distinctChars) of distinct characters.

Program 12.1 Count the distinct characters in a given string.

01 def distinct(str1):
02 '''
03 Objective: To determine unique characters in the given string
04 Input Parameters:
05 str1 - string value
06 Return value: str- string of unique characters
07 '''
08 str1 = str1.lower()
09 distinctChars = ''
10 for ch1 in str1:
11 if ch1 not in distinctChars:
12 distinctChars += ch1
13 return distinctChars
12.4.2 The Number of Common Characters in a Pair of Strings
To compute the count of matching characters in a pair of strings, let us develop a function findCommon() that takes
a pair of strings str1 and str2 as input parameters.
● On execution of line 9, the two strings may comprise a mix of upper and lowercase characters, we first construct a
string of lowercase characters.
● Line 10, we initialize the count of matching characters (count) in the two strings to zero.
● Next, using the function distinctChars, we first construct strings of unique characters from both strings.
● On execution of lines 12–15, The for-loop scans the two strings.

● or every character in the first string, we check whether there is a matching character in the second string.
F
● Line 13, if a matching character is found, we increment the count by 1 in line 14.
● On execution of line 15, finally, the function returns the count characters.

Program 12.2 The number of common characters in a pair of strings.

01 def findCommon(str1, str2):
02 '''
03 Objective: To find the number of common characters in a pair of strings
04 Input Parameters:
05 str1 - string value
06 str2 - string value
07 Return value: int- count
08 '''
09 str1, str2 = str1.lower(), str2.lower()
10 count = 0
11 uniqueStr1, uniqueStr2 = distinct(str1), distinct(str2)
12 for ch1 in uniqueStr1:
13 if ch1 in uniqueStr2 :
14 count += 1
15 return count
12.4.3 Searching for a Substring Within Another String
Let us write a function that searches for a substring in a given string and returns True if the substring is present in the
given string and False otherwise. To achieve this, let us develop a function isSubString() that takes two strings
(string and substr) as input parameters.

350 Touchpad Computer Science (Ver. 2.0)-XI