Python program to replace all occurrences of ‘a’ with $ in a string

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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

str = "Amdani athani kharcha rupaiya."

modified_str = ''

for char in range(0, len(str)):

    if(str[char] == 'a'):

        modified_str += '$'

    else:

        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

str = "An apple A day keeps doctor Away."

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)

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Sometimes, while working with Python strings, we can have a problem in which we need to replace all occurrences of a substring with other.

Input : test_str = “geeksforgeeks” s1 = “geeks” s2 = “abcd” 

Output : test_str = “abcdforabcd” Explanation : We replace all occurrences of s1 with s2 in test_str. 

Input : test_str = “geeksforgeeks” s1 = “for” s2 = “abcd” 

Output : test_str = “geeksabcdgeeks”

 Approach 1

We can use inbuilt function replace present in python3 to replace all occurrences of substring.

Implementation using the inbuilt function:-

Python3

input_string = "geeksforgeeks"

s1 = "geeks"

s2 = "abcd"

input_string = input_string.replace(s1, s2)

print(input_string)

Approach 2:

Splitting the string by substring and then replacing with the new string.split() function is used.

Python3

test_str="geeksforgeeks"

s1="geeks"

s2="abcd"

s=test_str.split(s1)

new_str=""

for i in s:

    if(i==""):

        new_str+=s2

    else:

        new_str+=i

print(new_str)

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)