You are given an integer array matches where matches[i] = [winneri, loseri] indicates that the player winneri defeated player loseri in a match.
Return a list answer of size 2 where:
answer[0] is a list of all players that have not lost any matches.
answer[1] is a list of all players that have lost exactly one match.
The values in the two lists should be returned in increasing order.
Note:
You should only consider the players that have played at least one match.
The testcases will be generated such that no two matches will have the same outcome.
Example 1:
Input: matches = [[1,3],[2,3],[3,6],[5,6],[5,7],[4,5],[4,8],[4,9],[10,4],[10,9]]
Output: [[1,2,10],[4,5,7,8]]
Explanation:
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].
Example 2:
Input: matches = [[2,3],[1,3],[5,4],[6,4]]
Output: [[1,2,5,6],[]]
Explanation:
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] = [].
Constraints:
1 <= matches.length <= 105
matches[i].length == 2
1 <= winneri, loseri <= 105
winneri != loseri
All matches[i] are unique.
Solutions
Solution 1: Hash Table + Sorting
We use a hash table cnt to record the number of matches each player has lost.
Then we traverse the hash table, put the players who lost 0 matches into ans[0], and put the players who lost 1 match into ans[1].
Finally, we sort ans[0] and ans[1] in ascending order and return the result.
The time complexity is $O(n \times \log n)$, and the space complexity is $O(n)$. Where $n$ is the number of matches.