6960번 - Common Words 스페셜 저지다국어

Given a sequence of $m$ words from a newspaper article and an integer $k$, find the $k^\text{th}$ most common word(s).

Input will consist of an integer $n$ followed by $n$ data sets. Each data set begins with a line containing $m$ and $k$, followed by $m$ lines, each containing a word of up to $20$ lowercase letters. There will be no more than $1\,000$ words per data set.

For each input data set, determine the $k^\text{th}$ most common word(s). To be precise, a word $w$ is the $k^\text{th}$ most common if exactly $k-1$ distinct words occur more frequently than $w$ in the data set. Note that $w$ might be multiply defined (i.e. there is a tie for the $k^\text{th}$ most common word) or $w$ might not exist (i.e. there is no $k^\text{th}$ most common word). For each data set, print a title line indicating $k$ using normal ordinal notation (1st, 2nd, 3rd, 4th, 5th, …) followed by a number of lines giving all the possible values for the $k^\text{th}$ most common word. A blank line should follow the last word for each data set.