2225. Find Players With Zero or One Losses

FindWinners.cs

public class Solution {
  public IList<IList<int>> FindWinners(int[][] matches) {
    var winnerDict = new Dictionary<int, int>();
    var loserDict = new Dictionary<int, int>();
    foreach(var m in matches){
      var winner = m[0];
      var loser = m[1];
      if(!winnerDict.ContainsKey(winner))
        winnerDict.Add(winner, 0);
      if(!loserDict.ContainsKey(loser))
        loserDict.Add(loser, 0);
      winnerDict[winner]++;
      loserDict[loser]++;
    }
    var winnersWithNoLost = winnerDict.Where(w=> !loserDict.ContainsKey(w.Key)).Select(w => w.Key).OrderBy(w => w).ToList();
    var exactlyOneLost = loserDict.Where(l => l.Value == 1).Select(l => l.Key).OrderBy(l => l).ToList();
    var ans = new List<IList<int>>();
    ans.Add(winnersWithNoLost);
    ans.Add(exactlyOneLost);
    return ans;
  }
}