Fix deque index wraparound overflow

[krotname]

Motivation

• Prevent integer overflow in prev() for extremely large capacities where the expression (i-1+cap) % cap can overflow to a negative value and lead to ArrayIndexOutOfBoundsException during deque operations.

Description

• Replace modulo-based wraparound in RingDeque.next and RingDeque.prev with branch-based increment/decrement logic (i++; return i == cap ? 0 : i; and i--; return i == -1 ? cap - 1 : i;) to preserve circular-buffer semantics without risking overflow.

Testing

• Compiled and ran the code with javac -d /tmp/codewars-classes src/main/java/algorithms/sprint2/Deque.java, executed the internal test via java -cp /tmp/codewars-classes -Dos.name=Windows -ea algorithms.sprint2.Deque which printed Test OK, exercised the sample CLI input via printf '4\n4\npush_front 861\npush_front -819\npop_back\npop_back\n' | java -cp /tmp/codewars-classes algorithms.sprint2.Deque, and ran a reflection-based DequePrevCheck that verifies prev(1_073_741_824) with cap=1_073_741_825, and all automated checks succeeded.

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Codex Task

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[krotname]

Superseded by the validated combined merge in #115: #115