Given a List. The task is to replace all the characters of the list with N except the given character.
Input : test_list = [‘G’, ‘F’, ‘G’, ‘I’, ‘S’, ‘B’, ‘E’, ‘S’, ‘T’], repl_chr = ‘*’, ret_chr = ‘G’
Output : [‘G’, ‘*’, ‘G’, ‘*’, ‘*’, ‘*’, ‘*’, ‘*’, ‘*’]
Explanation : All characters except G replaced by *Input : test_list = [‘G’, ‘F’, ‘G’, ‘B’, ‘E’, ‘S’, ‘T’], repl_chr = ‘*’, ret_chr = ‘G’
Output : [‘G’, ‘*’, ‘G’, ‘*’, ‘*’, ‘*’, ‘*’]
Explanation : All characters except G replaced by *
Method #1 : Using list comprehension + conditional expressions
In this, we perform the task of iteration using list comprehension, and replacements are taken care of using conditional operators.
Python3
# Python3 code to demonstrate working of# Replace all Characters Except K# Using list comprehension and conditional expressions# initializing liststest_list = ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T']# printing original listprint("The original list : " + str(test_list))# initializing repl_chrrepl_chr = '$'# initializing retain chararterret_chr = 'G'# list comprehension to remake list after replacementres = [ele if ele == ret_chr else repl_chr for ele in test_list]# printing resultprint("List after replacement : " + str(res)) |
The original list : ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T'] List after replacement : ['G', '$', 'G', '$', '$', '$', '$', '$', '$']
Time Complexity: O(n) where n is the number of elements in the list “test_list”.
Auxiliary Space: O(1) additional space is not needed.
In this, we use map() and lambda function to extend the logic to each element of the list.
Python3
# Python3 code to demonstrate working of# Replace all Characters Except K# Using map() + lambda# initializing liststest_list = ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T']# printing original listprint("The original list : " + str(test_list))# initializing repl_chrrepl_chr = '$'# initializing retain chararterret_chr = 'G'# using map() to extend logic to each element of listres = list(map(lambda ele: ret_chr if ele == ret_chr else repl_chr, test_list))# printing resultprint("List after replacement : " + str(res)) |
The original list : ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T'] List after replacement : ['G', '$', 'G', '$', '$', '$', '$', '$', '$']
Method 3: Using a for loop to iterate through the list and replace the characters accordingly
Python3
# Python3 code to demonstrate working of# Replace all Characters Except K# Using for loop# initializing liststest_list = ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T']# printing original listprint("The original list : " + str(test_list))# initializing repl_chrrepl_chr = '$'# initializing retain chararterret_chr = 'G'# creating an empty list to store the modified charactersres = []# iterating through the list and replacing the charactersfor ele in test_list: if ele == ret_chr: res.append(ele) else: res.append(repl_chr)# printing resultprint("List after replacement : " + str(res)) |
The original list : ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T'] List after replacement : ['G', '$', 'G', '$', '$', '$', '$', '$', '$']
Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), where n is the length of the input list, since we are creating a new list to store the modified characters.
Method #4 using the replace() function
Step-by-step approach
- Define the input list: test_list = [‘G’, ‘F’, ‘G’, ‘I’, ‘S’, ‘B’, ‘E’, ‘S’, ‘T’]
- Define the character to replace non-matching characters: repl_chr = ‘$’
- Define the character to retain: ret_chr = ‘G’
- Use a list comprehension to iterate over each element ele in the test_list.
- For each element, check if it is equal to ret_chr.
- If it is equal, replace it with ret_chr using the replace() function: ele.replace(ele, ret_chr).
- If it is not equal, replace it with repl_chr using the replace() function: ele.replace(ele, repl_chr).
- The resulting list of replaced characters is stored in res.
- Print the original list: print(“The original list:”, test_list).
- Print the list after replacement: print(“List after replacement:”, res).
Python3
test_list = ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T']repl_chr = '$'ret_chr = 'G'res = [ele.replace(ele, ret_chr) if ele == ret_chr else ele.replace (ele, repl_chr) for ele in test_list]print("The original list:", test_list)print("List after replacement:", res) |
The original list: ['G', 'F', 'G', 'I', 'S', 'B', 'E', 'S', 'T'] List after replacement: ['G', '$', 'G', '$', '$', '$', '$', '$', '$']
Time complexity: The time complexity of this method is O(n), where n is the length of the input list test_list.
Auxiliary space: The auxiliary space complexity is O(n), where n is the length of the input list.
