Python – Index Mapping Cypher

Sometimes, while working with Python, we can have problems in security or gaming domain, in which we need to create certain cyphers, they can be different types of. This includes Index Mapping Cypher in which we pass a string of integers and we get element characters in that order. Lets discuss certain ways to construct this. Method #1 : Using loop This is brute force manner in which this can be constructed. In this, we manually check for each character and map it as index number to value in string. 

Python3

# Python3 code to demonstrate working of
# Index Mapping Cypher
# Using loop

# initializing string
test_str = "geeksforgeeks"

# printing original string
print("The original string is : " + test_str)

# initializing cypher string
cyp_str = "53410"

# Index Mapping Cypher
# Using loop
res = ""
temp = [int(idx) for idx in cyp_str]
for ele in temp:
    res += test_str[ele]

# printing result
print("The deciphered value string : " + str(res))

Output : 

The original string is : geeksforgeeks
The deciphered value string : fkseg

Method #2 : Using join() + loop The combination of above functions can also be used to solve this problem. In this, we reduce a final loop by using join() to construct decipher string. 

Python3

# Python3 code to demonstrate working of
# Index Mapping Cypher
# Using loop + join()

# initializing string
test_str = "geeksforgeeks"

# printing original string
print("The original string is : " + test_str)

# initializing cypher string
cyp_str = "53410"

# Index Mapping Cypher
# Using loop + join()
res = [test_str[int(idx)] for idx in cyp_str]
res = ''.join(res)

# printing result
print("The deciphered value string : " + str(res))

Output : 

The original string is : geeksforgeeks
The deciphered value string : fkseg

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

Time Complexity: O(n)

Space Complexity: O(n)

Method 3 : using list comprehension.

 step-by-step approach

Initialize the string and the cipher string.
Convert the cipher string into a list of integers using list comprehension.
Use another list comprehension to map the indexes of the original string to the corresponding indexes in the cipher list.
Join the resulting list of characters into a single string.
Print the deciphered string.

Python3

# Initializing string
test_str = "geeksforgeeks"

# Printing original string
print("The original string is : " + test_str)

# Initializing cipher string
cyp_str = "53410"

# Index Mapping Cypher using list comprehension
res = ''.join([test_str[int(idx)] for idx in cyp_str])

# Printing result
print("The deciphered value string : " + str(res))

Output

The original string is : geeksforgeeks
The deciphered value string : fkseg

The time complexity of this method is O(n), where n is the length of the cipher string.

 The auxiliary space required is O(n), since we need to create a list of integers corresponding to the cipher string.