Group Words by First Letter with a Dictionary

Summary

Organize a list of words into groups keyed by their first letter (case-insensitive), preserving original order within groups.

Problem statement

Given a list of non-empty strings, group the words by their first letter in a case-insensitive way. The grouping key should be the lowercase version of the first character. Preserve the order of words as they appear in the input for each group's list. Return a dictionary where keys are single-character strings and values are lists of original words.

Task

Implement a function that groups non-empty words by their lowercase first character and returns a dictionary mapping each letter to the list of words that start with it, preserving input order.

Examples

Input format

A list of non-empty strings.

Output format

A dictionary mapping each lowercase first letter to a list of words (strings) that start with that letter.

Constraints

Words are non-empty strings. The function should be case-insensitive for grouping (use lowercase for keys). Preserve original word order in each group's list.

Samples