LeetCode192 solution

Printing out Word Frequency

The original problem is https://leetcode.com/problems/word-frequency/. In fact, counting word frequency is a typical application of bash. For example, Example 16-12 in this bash guide.

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LeetCode195 solution

Printing out Tenth Line

The original problem is https://leetcode.com/problems/tenth-line/. This is a basic application of bash: just get the 10th line from a file. Many methods can solve this simple question.

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LeetCode194 solution

How to transpose a file with bash

The original problem is https://leetcode.com/problems/transpose-file/. This question is difficult for one who is not familiar with the bash tools, such as awk. The first time I tried with a column-by-column handling with sed:

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LeetCode193 solution

Valid Phone Numbers

The original problem is https://leetcode.com/problems/valid-phone-numbers/. The basic problem here to match lines of telephone numbers in form of 123-456-789 (123) 456-789

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Regular expressions in bash

Using regular expressions(REs) is just like using REs in other common languages (C#, java, php, python...). REs in bash has two syntaxes, basic and extended, which are defined in IEEE POSIX standard. The basic syntax is the default mode in bash.

Commonly used metacharacters used in bash are

  • [ ]

    bracket expression. Used to match a selection of characters.

  • .

    dot sign matches any single character.

  • *, +, ?

    matches a preceding item zero or more times, one or more times, zero or one time, resp.

  • ^, $

    matches the empty string in the start, or the end of a line.

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