leetcode 192. Word Frequency

题目： 192. Word Frequency

解答：

cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -r | awk '{ print $2, $1 }'

tr -s: truncate（缩短） the string with target string, but only remaining one instance (e.g. multiple whitespaces)

把多个连续的空格缩短为一个空格，即只保留一个空格， 然后用’\n’替换空格。

cat words.txt | tr -s ' ' 多个连续的空格缩短为一个
cat words.txt | tr -s ' ' '*' 缩短后的一个空格被 ‘*’替换
uniqu -c

sort: To make the same string successive so that uniq could count the same string fully and correctly.

uniq -c: uniq is used to filter out the repeated lines which are successive, -c means counting

sort -r: -r means sorting in descending order

awk ‘{ print 2,1 }’: To format the output, see here.

练习：

cat testfile

world

boy

hello

zero

zero

zero

alive

alive

先排序再去重，结果如下。

cat testfile | sort | uniq

alive

boy

hello

world

zero

先排序再计数，结果如下

cat testfile | sort | uniq -c

2 alive

1 boy

1 hello

1 world

3 zero