Imports System
Module TrigramGenerator
'
' -------------------------------------------------------------------------
' What is a trigram?
' -------------------------------------------------------------------------
' A trigram is a sequence of exactly three consecutive characters taken
' from a word. To generate all trigrams, we slide a window of length 3
' across the string. Each step produces a new 3‑character slice.
'
' Example:
' Word: "magic"
' Trigrams: "mag", "agi", "gic"
'
' Trigrams are useful in text processing, search algorithms, and
' language modeling because they capture small structural patterns
' inside words.
'
'---------------------------------------------------------------------------
' Function: MakeTrigrams
' ----------------------
' Returns an array containing all trigrams of the given word.
'
' Steps:
' - If the word is shorter than 3 characters, return an empty array.
' - Otherwise, slide a window of size 3 across the word.
' - Use Substring() to extract each 3‑character sequence.
'
' The algorithm runs in O(n) time and uses O(n) space.
'---------------------------------------------------------------------------
Function MakeTrigrams(word As String) As String()
If word.Length < 3 Then
Return Array.Empty(Of String)()
End If
Dim count As Integer = word.Length - 2
Dim result(count - 1) As String
For i As Integer = 0 To count - 1
result(i) = word.Substring(i, 3)
Next
Return result
End Function
'---------------------------------------------------------------------------
' Main program:
' - Read a word from the user.
' - Generate trigrams.
' - Print each trigram.
'---------------------------------------------------------------------------
Sub Main()
Console.Write("Enter a word: ")
Dim input As String = Console.ReadLine()
Dim trigrams As String() = MakeTrigrams(input)
Console.WriteLine()
Console.WriteLine("Trigrams:")
For Each t In trigrams
Console.WriteLine(t)
Next
End Sub
End Module
'
' run:
'
' Enter a word: computer
'
' Trigrams:
' com
' omp
' mpu
' put
' ute
' ter
'
