H4ck3r Sp34k in Swift

Input:  "javascript is cool"

Output: "j4v45cr1pt 15 c00l"

Input:  "programming is fun"

Output: "pr0gr4mm1ng 15 fun"

Input:  "become a coder"

Output: "b3c0m3 4 c0d3r"

We have to iterate through every character of input, check for each scenario and treat it accordingly:

• Is it an 'a'? If so, replace with '4'. Otherwise:
• Is it an 'e'? If so, replace with '3'. Otherwise:
• Is it an 'i'? If so, replace with '1'. Otherwise:
• Is it an 'o'? If so, replace with '0'. Otherwise:
• Is it an 's'? If so, replace with '5'. Otherwise, keep it as it is.

Remember that strings are immutable. How does that affect us? How can we put this strategy into code?

Strings are immutable means you cannot directly change a character in a string like this: input[4] = '4'. This means we have to create a new string where we will store the solution as we create it. How can we translate these two hints in code?

Let's create a new string named solution, initially empty, where we will push all the encoded characters of input. We will use a for loop and a character variable c to iterate through input and treat the scenarios inside the loop:

solution = ""
for each c in input:
	if c == 'a':
        solution += '4'
    else if c == 'e':
        solution += '3'
    else if c == 'i':
        solution += '1'
    else if c == 'o':
        solution += '0'
    else if c == 's':
        solution += '5'
    else:
        solution += c
return solution

We have a for loop that performs exactly n iterations (n is the length of input), thus the Time Complexity is O(n).
The extra space we use is the extra string solution. Its length will be n in the end, thus the Extra Space used is also O(n).