Time Conversion Algorithm🕑🕝

In this article, I'll be describing how I solved the Time Conversion Challenge on HackerRank using Python 3.

This challenge is part of the Warmup challenges for the Algorithm section on HackerRank.

Problem 🎲

Given a time in 12-hour AM/PM format, convert it to military (24-hour) time.

Note:

• 12:00:00AM on a 12-hour clock is 00:00:00 on a 24-hour clock.
• 12:00:00PM on a 12-hour clock is 12:00:00 on a 24-hour clock.

Example

- s = '12:01:00PM': 
   Return '12:01:00'.

- s = '12:01:00AM': 
   Return '00:01:00'.

Function Description

Complete the timeConversion function in the editor. It should return a new string representing the input time in 24-hour format.

timeConversion has the following parameter(s):

• string s: a time in 12-hour format

Returns

• string: the time in 24-hour format

Input Format

A single string s that represents a time in 12-hour clock format (i.e.: hh:mm:ssAM or hh:mm:ssPM)

Constraints

• All input times are valid

Samle Input:

'07:05:45PM'

Samle Ouput:

'19:05:45'

Solution 🔎

As always, we will start by breaking the problem into smaller bits and solving each bit synchronously.

Let's assume s = '12:01:00AM' to test our solution.

def timeConversion(s):
    # Write your code here

Step 1️⃣ : Slicing and splitting the input string into two parts. 🔪

• Since we are given the time format in a string of constant length, we can split all characters minus the last two (i.e. PM or AM).
• This means splitting the string s by the delimiter : and slicing the first 8 characters.
• Let's store the sliced array showing only digits in a variable, a.
• and store the time format part of the array in a variable,tf.

  a = s[:8].split(":") 
  >> ['12', '01', '00']
  tf = s[-2:]
  >> AM
  

Step 2️⃣: String array to int array ⚙️

• We need to convert this string array (containing digits) into an integer array, so we can easily manipulate them in our time conversion logic 🤓.
• To achieve this, we use python's map function.

  map(function, iterable, ...) returns an iterator that applies a function to every item of iterable, yielding the result.

a = list(map(int, a))
>> [12, 1, 0]

• Here, we called the int function on every item in the array and converted the result to a list.

Step 3️⃣: Time conversion logic time!⏱️

• We use conditional statements to implement our logic.
• Here, we'll do the following:
  • Return hh + 12, if the time is PM and not 12 (all digits from 0 - 11),

    example: return 17 if its 5PM.

  • Return hh - 12, if the time is AM and 12,

    example: return 0 if its 12AM.

  • Return the same value in all other cases (example in mm digits).

    if tf == 'PM' and a[0] != 12: a[0]+=12 
    elif tf == 'AM' and a[0]==12: a[0]-=12
    >>
    

Step 4️⃣: Convert our manipulated int array back to a string array.

• Here, we'll convert our int array (after applying our time conversion logic) back to a string array (temporarily store its items in a variable b, while also maintaining leading zeroes using python's .zfill() function
• Then, store our new strings in a new string array called a_new.

  b = list(map(str, a))
    for num in b: 
        a_new.append(num.zfill(2))
  >> ['00', '01', '00']
  

Step 5️⃣: Return our string array in the desired string format. 🥅

• Let's convert our string array back to the desired HH:SS:MM format using python's join() function
• Finally, we return the string in a variable, ouput.

  output = ':'.join(a_new)
    return output
  >> 00:01:00
  

Full code:

def timeConversion(s):
    # Write your code here
    a = s[:8].split(":")
    a = list(map(int, a))

    tf = s[-2:]

    if tf == 'PM' and a[0] != 12: a[0]+=12
    elif tf == 'AM' and a[0]==12: a[0]-=12

    b = list(map(str, a))
    a_new = []
    for num in b:
        a_new.append(num.zfill(2))

    output = ':'.join(a_new)

    return output



timeConversion('12:01:00AM')

Hope this helps with understanding this challenge. Happy Coding!👨🏽‍💻