[Programmers] Filename Sort

https://programmers.co.kr/learn/courses/30/lessons/17686

Approach 1

We need to split filenames based on numeric characters. One way is to implement it manually:

1
number_list = [str(i) for i in range(10)]
2

3
for idx in range(len(files)):
4
    head, number, tail = "", "", ""
5
    number_idx, tail_idx = -1, -1
6
    # Find the start index of the number part
7
    for j in range(len(files[idx])):
8
        if files[idx][j] in number_list:
9
            head = files[idx][:j]
10
            # print(head)
11
            number_idx = j
12
            break
13
    # Find the start index of the tail part
14
    for j in range(number_idx, len(files[idx])):
15
        if files[idx][j] not in number_list:
16
            number = int(files[idx][number_idx:j])
17
            break
18
    tail = files[idx][j:]
19
    files[idx] = [head, number, tail]

Midway through implementing this, I remembered regex. Since \d can distinguish digits, we can do:

1
re.compile(r'(\d+)')

Since we only need to split, I used re.split.

For sorting, passing the priority to the sort function handles everything. Since we only need to sort by head and number, I pass this lambda as the sort key:

1
lambda x: (x[0].lower(), int(x[1]))

Approach 2

Apparently you could also use Java’s Comparable interface for this. In Python, you’d implement __cmp__, though there’s no real reason to use it for this problem. It might be useful if the sorting logic were more complex.

Code

https://github.com/naem1023/codingTest/blob/master/sort/pg-30-17686.py