shell之計算文本中單詞出現頻率

Word Frequency（https://leetcode.com/problems/word-frequency/description/）

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

而後來看看強大的 awk

awk -vRS='( |\n)+' '{a[$0]++}END{for(i in a)m[a[i]]=i;i=asort(a);for(;i;)print m[a[i]],a[i--]}' words.txt