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Quick Summary
Generate all valid letter combinations from a digit string using a custom phone keypad mapping.
Consecutive identical digits can be grouped, where the group size selects the corresponding letter from the mapping.
Systematically explore all valid groupings and letter selections using recursion.
What This Tests
Recursive backtracking and decision tree exploration
String partitioning and dynamic index tracking
Constraint validation during state transitions
Combinatorial generation techniques
Common Patterns
Backtracking
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Python3
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Input
digits =
Output
Expected
