Reorder Log Files

Problem

Reorder logs. Here are the rules.

The first part of the log is the identifier.
A log that consists of alphabets comes before the ones with numbers.
The identifier does not affect the order, but when the remaining characters are same, it should be sorted by the identifier.
As for the number logs, you should maintain their relative order.

Examples

example.py

log1 = ["dig1 8 1 5 1", "let1 art can", "dig2 3 6", "let2 own kit dig", "let3 art zero"]
output1 = ["let1 art can", "let3 art zero", "let2 own kit dig", "dig1 8 1 5 1", "dig2 3 6"]

log2 = ["a1 9 2 3 1", "g1 act car", "zo4 4 7", "ab1 off key dog", "a8 act zoo"]
output2 = ["g1 act car", "a8 act zoo", "ab1 off key dog", "a1 9 2 3 1", "zo4 4 7"]

Things you should know

Lambda function

If you have used another programming languages that support lambda functions
Here's a good news. There also is one in Python too!

arrow-function.js

const add = (num1, num2) => num1 + num2;

lambda.py

# normal case
add = lambda num1, num2: num1 + num2

# when there is no argument
greeting = lambda: 'hello'

Sorting

You can easily sort a list using built-in sort function.

sorting.py

numbers = [3, 2, 1]

numbers.sort() 
print(numbers) # [1, 2, 3]

But the thing is, this sort function changes the order of original list.
If you want the original to stay the same, You can use sorted function.

sorting.py

numbers = [3, 2, 1]

new_numbers = sorted(numbers) 
print(new_numbers) # [1, 2, 3]
print(numbers) # [3, 2, 1]

One more thing, let's assume you somehow want to sort a list of object.
You can do this by explicitly setting the key by which the list will be sorted.
Also you can sort in a reversed order by setting reverse=True.

sorting.py

people = [
    {
        'name': 'sam',
        'age': 30
    },
    {
        'name': 'alex',
        'age': 19
    },
    {
        'name': 'john',
        'age': 25
    }
]

oldest_first = sorted(people, key=lambda x: x['age'], reverse=True)
print(oldest_first) # sam -> john -> alex

Solutions

main.py

def reorder_log_files(logs: List[str]) -> List[str]:
    digits = []
    letters = []

    for log in logs:
        if log.split()[1].isdigit():
            digits.append(log)
        else:
            letters.append(log)

    return sorted(letters, key=lambda x: (x.split()[1:], x.split()[0])) + digits

Problem

Examples

Things you should know

Lambda function

Sorting

Solutions

References