using System;
using System.Collections.Generic;
/*
Efficient algorithm using bitmasking:
------------------------------------
Each letter 'a'..'z' is represented by one bit in a 32-bit int.
bit 0 -> 'a'
bit 1 -> 'b'
...
bit 25 -> 'z'
For each word:
- Set the bit corresponding to each letter.
Then:
- Intersect all bitmasks using bitwise AND.
The remaining bits represent letters common to all words.
This avoids sorting, dynamic memory, and repeated scanning.
*/
class CommonLettersProgram
{
// Convert a word into a bitmask of its letters
static int WordToMask(string word)
{
int mask = 0;
foreach (char c in word) {
if (c >= 'a' && c <= 'z') {
mask |= (1 << (c - 'a')); // set bit for this letter
}
}
return mask;
}
// Compute common letters across all words
static int CommonLetters(List<string> words)
{
if (words.Count == 0) return 0;
int common = WordToMask(words[0]);
for (int i = 1; i < words.Count; i++) {
common &= WordToMask(words[i]); // bitwise intersection
}
return common;
}
// Print letters represented by a bitmask
static void PrintMaskLetters(int mask)
{
for (int i = 0; i < 26; i++) {
if ((mask & (1 << i)) != 0) {
Console.Write((char)('a' + i) + " ");
}
}
Console.WriteLine();
}
static void Main()
{
List<string> words = new List<string>
{
"algebraic",
"alphabetic",
"ambiance",
"abacus",
"metabolic",
"parabolic",
"playback",
"drawback",
"fabricate",
"flashback",
"syllabic"
};
int result = CommonLetters(words);
Console.WriteLine("Common letters across all words:");
PrintMaskLetters(result);
}
}
/*
run:
Common letters across all words:
a b c
*/
