LeetCode Shell Problems

195. Tenth Line -- 第十行

How would you print just the 10th line of a file?

Solution:

awk 'NR==10' file.txt

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194. Transpose File -- 转置文件

Given a text file file.txt, transpose its content.
You may assume that each row has the same number of columns and each field is separated by the ' ' character.
For example, if file.txt has the following content:
name age
alice 21
ryan 30
Output the following:
name alice ryan
age 21 30

Solution:

awk '{  
    max_nf = NF  
    max_nr = NR  
    for (x = 1; x <= NF; x++) {  
        vector[x, NR] = $x  
    }  
}  
END {  
for (x = 1; x <= max_nf; x++) {  
    for (y = 1; y <= max_nr; y++) {  
        printf("%s", vector[x, y])  
        if (y < max_nr)  
            printf(" ")  
    }  
    if (x < max_nf)  
        printf("\n")  
}  
}' file.txt

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193. Valid Phone Numbers -- 有效电话号码

Given a text file file.txt that contains list of phone numbers (one per line), write a one liner bash script to print all valid phone numbers.
You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)
You may also assume each line in the text file must not contain leading or trailing white spaces.
For example, assume that file.txt has the following content:
987-123-4567
123 456 7890
(123) 456-7890
Your script should output the following valid phone numbers:
987-123-4567
(123) 456-7890

Solution:

awk '/^[0-9]{3}-[0-9]{3}-[0-9]{4}$/ || /^\([0-9]{3}\) [0-9]{3}-[0-9]{4}$/' file.txt

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192. Word Frequency -- 词频

Write a bash script to calculate the frequency of each word in a text file words.txt.
For simplicity sake, you may assume:

• words.txt contains only lowercase characters and space ' ' characters.
• Each word must consist of lowercase characters only.
• Words are separated by one or more whitespace characters.

For example, assume that words.txt has the following content:
the day is sunny the the
the sunny is is
Your script should output the following, sorted by descending frequency:
the 4
is 3
sunny 2
day 1
Note:
Don't worry about handling ties, it is guaranteed that each word's frequency count is unique.

Solution:

awk '{for(i=1;i<=NF;i++) a[$i]+=1} END{for(i in a) print i,a[i] | "sort -r -n -k2"}' words.txt