Formatted question description: https://leetcode.ca/all/2225.html

# 2225. Find Players With Zero or One Losses (Medium)

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.


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.


Constraints:

• 1 <= matches.length <= 105
• matches[i].length == 2
• 1 <= winneri, loseri <= 105
• winneri != loseri
• All matches[i] are unique.

Companies:
Indeed

Related Topics:
Graph

Similar Questions:

## Solution 1. Hash Set and Map

Traverse the array, store the unique winners in a set win and store a mapping from person to lose count in map lose.

Traverse lose map, for each pair person, cnt, add person to vector oneLose if cnt == 1 (i.e. this person loses exactly once), and erase this person from win.

Lastly, return the elements in win and oneLose.

// OJ: https://leetcode.com/problems/find-players-with-zero-or-one-losses/
// Time: O(NlogN)
// Space: O(N)
class Solution {
public:
vector<vector<int>> findWinners(vector<vector<int>>& A) {
set<int> win;
map<int, int> lose; // person, count
for (auto &m : A) {
win.insert(m[0]);
lose[m[1]]++;
}
vector<int> oneLose;
for (auto &[p, cnt] : lose) {
if (cnt == 1) oneLose.push_back(p);
win.erase(p);
}
return {vector<int>(begin(win), end(win)), oneLose};
}
};


## Discuss

https://leetcode.com/problems/find-players-with-zero-or-one-losses/discuss/1908802/