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Problem solution · SQL

Find Circular Gift Exchange Chains

Find Circular Gift Exchange Chains: a SQL solution using depth-first search. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Depth-first search
Source
walkccc LeetCode Solutions
Length
32 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Depth-first search

For Find Circular Gift Exchange Chains, the implementation follows one branch at a time, making it suitable for components, trees, backtracking, or dependency exploration.

  1. Define the state carried into one recursive or stack frame.
  2. Mark or choose the current state before exploring children.
  3. Combine child results or undo the choice when the branch finishes.

Code notes

  • 32 lines of SQL from the credited upstream file 3401.sql.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Count unique states for graph traversal; for backtracking, count the branching factor and maximum depth.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeFind Circular Gift Exchange Chains · SQLSQL
Use this to learn the idea, then write your own version.
WITH RECURSIVE  Chains AS (    SELECT *, giver_id AS start_id    FROM SecretSanta    UNION ALL    SELECT SecretSanta.*, Chains.start_id    FROM SecretSanta    INNER JOIN Chains      ON (        SecretSanta.giver_id = Chains.receiver_id        AND SecretSanta.giver_id != Chains.start_id) -- Avoid cycles.  ),  ChainSummary AS (    SELECT      start_id,      COUNT(*) AS chain_length,      SUM(gift_value) AS total_gift_value    FROM Chains    GROUP BY 1  ),  UniqueChains AS (    SELECT DISTINCT chain_length, total_gift_value    FROM ChainSummary  )SELECT  RANK() OVER(    ORDER BY chain_length DESC, total_gift_value DESC  ) AS chain_id,  chain_length,  total_gift_valueFROM UniqueChains;

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