Python Program to Replace all Occurrences of ‘a’ with $ in a String

Given a string, the task is to write a Python program to replace all occurrence of ‘a’ with $.

Examples:

Input: Ali has all aces
Output: $li h$s $ll $ces

Input: All Exams are over
Output: $ll Ex$ms $re Over

The first approach uses splitting of the given specified string into a set of characters. An empty string variable is used to store modified string . We loop over the character array and check if the character at this index is equivalent to ‘a’ , and then append ‘$’ sign, in case the condition is satisfied. Otherwise, the original character is copied into the new string.  

Python3

# declaring a string variable
str = "Amdani athani kharcha rupaiya."

# declaring an empty string variable for storing modified string
modified_str = ''

# iterating over the string
for char in range(0, len(str)):
    # checking if the character at char index is equivalent to 'a'
    if(str[char] == 'a'):
        # append $ to modified string
        modified_str += '$'
    else:
        # append original string character
        modified_str += str[char]

print("Modified string : ")
print(modified_str)

Output:

Modified string :
$md$ni $th$ni kh$rch$ rup$iy$.

The second approach uses the inbuilt method replace() to replace all the occurrences of a particular character in the string with the new specified character. The method has the following syntax : 

replace( oldchar , newchar)

This method doesn’t change the original string, and the result has to be explicitly stored in the String variable. 

Python3

# declaring a string variable
str = "An apple A day keeps doctor Away."

# replacing character a with $ sign
str = str.replace('a', '$')
print("Modified string : ")
print(str)

Output:

Modified string :
$n $pple $ d$y keeps doctor $w$y.

The time and space complexity for all the methods are the same:

Time Complexity: O(n)

Space Complexity: O(n)