Group words that map to same phone digits

Q: Group words that map to same phone digits

This question evaluates string processing, mapping and grouping competencies and the ability to design efficient encodings for detecting collisions, assessing practical application of algorithmic techniques. It is commonly asked in the Coding & Algorithms domain because it probes algorithmic efficiency, data-structure selection, and handling of input-size and performance constraints.

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Question

Problem

On a classic phone keypad (T9), letters map to digits:

2: ABC , 3: DEF , 4: GHI , 5: JKL ,
6: MNO , 7: PQRS , 8: TUV , 9: WXYZ

Given a list of lowercase words, convert each word into its digit string (e.g., "tree" -> "8733").

Return all groups of words that map to the same digit string (i.e., collisions). Only include groups of size >= 2.

Input / Output

Input: words: string[] (lowercase a–z)
Output: A list of groups, where each group is a list of words sharing the same digit encoding.

Constraints (typical)

1 <= len(words) <= 2 * 10^5
1 <= len(word) <= 30

Examples

Input: ["tree", "used", "apple", "vase"]
- tree -> 8733 , used -> 8733 , apple -> 27753 , vase -> 8273
- Output: [["tree", "used"]]

Group words that map to same phone digits

Quick Overview

Problem

Input / Output

Constraints (typical)

Examples

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