# Reorder Data in Log Files

Published: Sep 9, 2022

Medium Sorting Array String

## Introduction

This is just a sorting problem. However, some clever comparator is required.

## Problem Description

You are given an array of `logs`. Each log is a space-delimited string of words, where the first word is the identifier.

There are two types of logs:

• Letter-logs: All words (except the identifier) consist of lowercase English letters.
• Digit-logs: All words (except the identifier) consist of digits.

Reorder these logs so that:

1. The letter-logs come before all digit-logs.
2. The letter-logs are sorted lexicographically by their contents. If their contents are the same, then sort them lexicographically by their identifiers.
3. The digit-logs maintain their relative ordering.

Return the final order of the logs.

Constraints:

• `1 <= logs.length <= 100`
• `3 <= logs[i].length <= 100`
• All the tokens of `logs[i]` are separated by a single space.
• `logs[i]` is guaranteed to have an identifier and at least one word after the identifier.

https://leetcode.com/problems/reorder-data-in-log-files/

## Examples

``````Example 1:
Input: logs = ["dig1 8 1 5 1","let1 art can","dig2 3 6","let2 own kit dig","let3 art zero"]
Output: ["let1 art can","let3 art zero","let2 own kit dig","dig1 8 1 5 1","dig2 3 6"]
Explanation:
The letter-log contents are all different, so their ordering is "art can", "art zero", "own kit dig".
The digit-logs have a relative order of "dig1 8 1 5 1", "dig2 3 6".
``````
``````Example 2:
Input: logs = ["a1 9 2 3 1","g1 act car","zo4 4 7","ab1 off key dog","a8 act zoo"]
Output: ["g1 act car","a8 act zoo","ab1 off key dog","a1 9 2 3 1","zo4 4 7"]
``````

## Analysis

The Python solution relies on a tuple sorting feature. While sorting the tuple, the first element, the second element if the first is the same will be used to compare. The custom comparator returns `(1,)` for digit logs so that digit logs come later. For letter logs, it returns `(0, string except id, id)` to comply with the condition. With this custom comparator, just soring the log gives us the answer.

The C++ solution relies on the stable_sort function. The custom comparator logic is similar to the Python’s.

## Solution

``````class ReorderDataInLogFiles {
public:
vector<string> reorderLogFiles(vector<string>& logs) {
stable_sort(logs.begin(), logs.end(),
[](const string &a, const string &b) {
if (isdigit(a.back())) return false;
if (isdigit(b.back())) return true;
const string aa = a.substr(a.find(' '));
const string bb = b.substr(b.find(' '));
if (aa == bb) return a < b;
return aa < bb;
});
return logs;
}
};
``````
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``````class ReorderDataInLogFiles:
def reorderLogFiles(self, logs: List[str]) -> List[str]:
def comp(log):
id_, rest = log.split(' ', 1)
if rest[0].isdigit():
return (1, )
else:
return (0, rest, id_)
return sorted(logs, key=comp)
``````
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``````

## Complexities

• Time: `O(n * log(n))`
• Space: `O(1)`