2225. Find Players With Zero or One Losses

MediumView on LeetCode

Array Hash Table Sorting Counting

Time: O(n)

Space: O(n)

Problem Overview

Count wins per team from match results.

Intuition

Count wins per team from match results. Track frequency in a map; find maximum win count; return all teams tied at that maximum (sorted by index or name per problem).

Algorithm

1Initialize wins map.
2For each match [winner, loser]: wins[winner]++.
3Find maxWin = max of map values.
4Collect all teams with wins[team] == maxWin into result list.
5Return result (often sorted by team index).

Example Walkthrough

Input: matches with Alice/Bob wins

1.Tally wins per name.
2.Return every team with the highest tally.

Output: list of top teams

Common Pitfalls

•Losers are not inserted unless they win elsewhere.
•Ties return multiple teams.
•Team ids may be integers — map accordingly.

2225.cs

// Approach: HashMap tracking loss counts; separate players with 0 and exactly 1 loss.
// Time: O(n) Space: O(n)

public class Solution
{
    public IList<IList<int>> FindWinners(int[][] matches)
    {
        var wmap = new Dictionary<int, int>();
        var lmap = new Dictionary<int, int>();

        foreach (int[] match in matches)
        {
            int winner = match[0];
            int loser = match[1];
            if (wmap.ContainsKey(winner))
                wmap[winner]++;
            else
                wmap.Add(winner, 1);

            if (lmap.ContainsKey(loser))
                lmap[loser]++;
            else
                lmap.Add(loser, 1);
        }

        var lostOnlyOne = new List<int>();
        foreach (var kvp in lmap)
        {
            if (kvp.Value == 1)
                lostOnlyOne.Add(kvp.Key);
        }
        lostOnlyOne.Sort();

        var neverLost = new List<int>();
        foreach (var kvp in wmap)
        {
            if (!lmap.ContainsKey(kvp.Key))
                neverLost.Add(kvp.Key);
        }
        neverLost.Sort();

        var ans = new List<IList<int>>();
        ans.Add(neverLost);
        ans.Add(lostOnlyOne);

        return ans;
    }
}

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