using System;
using System.Collections.Generic;
using System.Text;
class CommonWordsProgram
{
/*
Normalize a string:
- Convert letters to lowercase
- Replace any non-letter with a space
This ensures consistent word comparison.
*/
static string Normalize(string input)
{
var sb = new StringBuilder(input.Length);
foreach (char ch in input) {
if (char.IsLetter(ch))
sb.Append(char.ToLower(ch));
else
sb.Append(' ');
}
return sb.ToString();
}
/*
Extract words from a string.
This function:
- Normalizes the input
- Splits on whitespace
- Filters out empty entries
- Returns a HashSet<string> for fast lookup and automatic duplicate removal
*/
static HashSet<string> ExtractWords(string input)
{
string normalized = Normalize(input);
string[] parts = normalized.Split(' ', StringSplitOptions.RemoveEmptyEntries);
var words = new HashSet<string>(StringComparer.Ordinal);
foreach (string w in parts)
words.Add(w);
return words;
}
/*
Find common words between two strings.
This function:
- Extracts words from both strings
- Uses set intersection for efficiency
- Returns a new HashSet<string> containing the common words
*/
static HashSet<string> FindCommonWords(string a, string b)
{
var wordsA = ExtractWords(a);
var wordsB = ExtractWords(b);
var common = new HashSet<string>(wordsA, StringComparer.Ordinal);
common.IntersectWith(wordsB);
return common;
}
static void Main()
{
string s1 = "The quick brown fox jumps over the lazy dog.";
string s2 = "A lazy dog sleeps while the quick fox runs away.";
var common = FindCommonWords(s1, s2);
Console.WriteLine("Common words:");
foreach (string w in common)
Console.WriteLine(w);
}
}
/*
run:
Common words:
the
quick
fox
lazy
dog
*/
