Players with No Losses or Exactly One Loss
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
Each row `[winner, loser]` in `matches` records one match result. Consider only players who appear in at least one row. Return two lists in this order: players with no losses, then players with exactly one loss. Each list must be in increasing player-ID order. No ordered match result is repeated.
```cpp
class Solution {
public:
vector<vector<int>> findWinners(vector<vector<int>>& matches);
};
```
### Examples
**Example 1:**
```text
matches = [[1,2],[3,2],[3,4]]
Output: [[1,3],[4]]
Explanation: Player 2 lost twice, player 4 once, and 1 and 3 never lost.
```
**Example 2:**
```text
matches = [[2,1],[1,2]]
Output: [[],[1,2]]
Explanation: Each player lost exactly once.
```
### Constraints
- `1 <= matches.length <= 10^5`.
- Every pair has different player IDs in `[1,10^5]`; all ordered pairs are unique.
### Clarifying Questions
Unseen IDs are excluded. Reverse outcomes [a,b] and [b,a] are different matches. Both output lists require increasing order.
```hint Inspect the structure
How can a winner who never appears as a loser still get an entry in the loss table?
```
### Reasoning checkpoints
- Include only observed players and count losses without discarding earlier results after a later win.
- Separate zero-loss and exactly-one-loss players, excluding players with more losses.
- Return both lists in the required increasing order, including an empty list when appropriate.
### Optional extensions
How could you also report the number of wins for each participating player?
Overview: Players with No Losses or Exactly One Loss. Each pair in matches is [winner,loser]. Consider only players appearing in at least one match. Return two increasing lists: players who never lost, then players who lost exactly once. Each ordered match outcome is unique.