LeetCode Shell 解题集合

LeetCode Shell 的试题多为文本操作，195. Tenth Line、193. Valid Phone Numbers、192. Word Frequency、194. Transpose File 暂时只有 4 道题，就整合在这一起了

Shell 中文本处理的事情基本 awk sed grep sort uniq tail head 几个命令组合组合就搞定了

195. Tenth Line

大体意思

How would you print just the 10th line of a file?
For example, assume that file.txt has the following content:

Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10

Your script should output the tenth line, which is:

Line 10

打印出文本文件中第 10 行的内容。

自己的解法

cat  file.txt | tail -n +10 | head -n 1

这是学习了：linux 如何显示一个文件的某几行(中间几行) - 香格里拉(^o^)/

别人的解法

方法一：

awk 'NR==10' file.txt
# awk的默认动作就是打印$0，所以NR==10后面可以不用加{print $0}

方法二：

sed -n '10p' file.txt
# 如果不够10行，则什么也不打印

方法三：

line=$(cat file.txt | wc -l)     # 千万注意，等号前后一定不要有空格
if [ "$line" -ge 10 ] ; then     # $line的双引号也可以不用加
  cat file.txt | head -n 10 | tail -n 1
fi

Reference: leetcode-195 Tenth Line - 2> /dev/null

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

匹配有效的电话号码

自己的解法

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

别人的解法

grep -P '^(\(\d{3}\)|\d{3}-)\d{3}-\d{4}$' file.txt

Reference: LeetCode 193: Valid Phone Numbers – Revo

192. Word Frequency

大体意思

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.

统计单词出现的频次，然后倒序排列

别人的解法

awk '{i=1;while(i<=NF){print $i;i++}}' words.txt  | sort | uniq -c  | sort -k1nr  | awk '{print $2 " " $1}'

1、利用 awk 默认一行一条记录，默认以空格划分每条记录，NF 为划分的总块数先打印出所有单词
2、排序 + 统计 + 消除重复
3、输出

Reference: LeetCode 192 Word Frequency - wangxiaobupt 的专栏

awk '
{ for (i=1; i<=NF; i++) { ++S[$i]; } }
END { for (i in S) { print i, S[i] } }
' words.txt | sort -nr -k 2

Reference: leetcode/solutions/192.Word_Frequency at master · illuz/leetcode

194. Transpose File

大体意思

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

别人的解法

awk '
{
    for (i = 1; i <= NF; i++) {
        if(NR == 1) {
            s[i] = $i;
        } else {
            s[i] = s[i] " " $i;
        }
    }
}
END {
    for (i = 1; s[i] != ""; i++) {
        print s[i];
    }
}' file.txt

Reference: leetcode/solutions/194.Transpose_File at master · illuz/leetcode

总结

Shell 中文本处理的事情基本 awk sed grep sort uniq tail head 几个命令组合组合就搞定了，各命令的常用方法之后总结