feat(graph): add DSU-based account merge algorithm

[nickzerjeski]

Description

Add an account merge implementation using Disjoint Set Union (Union-Find).

Fixes #6831

Changes

• Added AccountMerge.mergeAccounts(List<List<String>>) in com.thealgorithms.graph.
• Uses path compression + union by rank to merge accounts sharing at least one email.
• Added tests for:
  • merging shared-email accounts
  • same-name accounts without shared email staying separate
  • empty input

Validation

• mvn -q -Dtest=AccountMergeTest test

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.82759% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.53%. Comparing base (79bc620) to head (b9e1672).

Files with missing lines	Patch %	Lines
...ain/java/com/thealgorithms/graph/AccountMerge.java	94.82%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7377      +/-   ##
============================================
+ Coverage     79.50%   79.53%   +0.03%     
- Complexity     7161     7175      +14     
============================================
  Files           797      798       +1     
  Lines         23409    23467      +58     
  Branches       4603     4617      +14     
============================================
+ Hits          18611    18665      +54     
- Misses         4054     4055       +1     
- Partials        744      747       +3     

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[Copilot]

Pull request overview

Adds a Disjoint Set Union (Union-Find) based solution for the “merge accounts by shared email” problem under com.thealgorithms.graph, along with JUnit tests. The PR also introduces a new geometry utility for 2D line segment intersection (with tests) and extends binary search test coverage for null inputs.

Changes:

• Added AccountMerge.mergeAccounts(...) implementing account merging via DSU (path compression + union by rank).
• Added AccountMergeTest covering shared-email merges, same-name/no-shared-email separation, and empty input.
• Added LineIntersection + LineIntersectionTest, and extended IterativeBinarySearchTest for null array/key cases.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/main/java/com/thealgorithms/graph/AccountMerge.java	New DSU-based account merging implementation.
src/test/java/com/thealgorithms/graph/AccountMergeTest.java	Tests for account merging behavior and ordering.
src/main/java/com/thealgorithms/geometry/LineIntersection.java	New geometry utility for segment intersection + intersection point computation.
src/test/java/com/thealgorithms/geometry/LineIntersectionTest.java	Tests for segment intersection and computed intersection point.
src/test/java/com/thealgorithms/searches/IterativeBinarySearchTest.java	Added tests for null array and null key behavior.

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[DenizAltunkapan]

@nickzerjeski why did you choose the graphs package for this type of algorithm? Could you please look up whether there is a better option?

[nickzerjeski]

@DenizAltunkapan I placed AccountMerge in com.thealgorithms.graph because this is fundamentally a connectivity/components problem on an implicit graph (emails/accounts), while Union-Find is the implementation technique. Also, issue #6831 requested adding this in the Graph section. But if you prefer a different organization, I can move it.