Find Players With Zero or One Losses
<p>You are given an integer array <code>matches</code> where <code>matches[i] = [winner<sub>i</sub>, loser<sub>i</sub>]</code> indicates that the player <code>winner<sub>i</sub></code> defeated player <code>loser<sub>i</sub></code> in a match.</p>

<p>Return <em>a list </em><code>answer</code><em> of size </em><code>2</code><em> where:</em></p>

<ul>
	<li><code>answer[0]</code> is a list of all players that have <strong>not</strong> lost any matches.</li>
	<li><code>answer[1]</code> is a list of all players that have lost exactly <strong>one</strong> match.</li>
</ul>

<p>The values in the two lists should be returned in <strong>increasing</strong> order.</p>

<p><strong>Note:</strong></p>

<ul>
	<li>You should only consider the players that have played <strong>at least one</strong> match.</li>
	<li>The testcases will be generated such that <strong>no</strong> two matches will have the <strong>same</strong> outcome.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> matches = [[1,3],[2,3],[3,6],[5,6],[5,7],[4,5],[4,8],[4,9],[10,4],[10,9]]
<strong>Output:</strong> [[1,2,10],[4,5,7,8]]
<strong>Explanation:</strong>
Players 1, 2, and 10 have not lost any matches.
Players 4, 5, 7, and 8 each have lost one match.
Players 3, 6, and 9 each have lost two matches.
Thus, answer[0] = [1,2,10] and answer[1] = [4,5,7,8].
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> matches = [[2,3],[1,3],[5,4],[6,4]]
<strong>Output:</strong> [[1,2,5,6],[]]
<strong>Explanation:</strong>
Players 1, 2, 5, and 6 have not lost any matches.
Players 3 and 4 each have lost two matches.
Thus, answer[0] = [1,2,5,6] and answer[1] = [].
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= matches.length &lt;= 10<sup>5</sup></code></li>
	<li><code>matches[i].length == 2</code></li>
	<li><code>1 &lt;= winner<sub>i</sub>, loser<sub>i</sub> &lt;= 10<sup>5</sup></code></li>
	<li><code>winner<sub>i</sub> != loser<sub>i</sub></code></li>
	<li>All <code>matches[i]</code> are <strong>unique</strong>.</li>
</ul>
Array; Hash Table; Counting; Sorting
func findWinners(matches [][]int) [][]int {
	cnt := map[int]int{}
	for _, e := range matches {
		if _, ok := cnt[e[0]]; !ok {
			cnt[e[0]] = 0
		}
		cnt[e[1]]++
	}
	ans := make([][]int, 2)
	for x, v := range cnt {
		if v < 2 {
			ans[v] = append(ans[v], x)
		}
	}
	sort.Ints(ans[0])
	sort.Ints(ans[1])
	return ans
}