3227. Vowels Game in a String
Approach
Count vowels; Alice wins if count is odd or nonzero (she can always take advantage).
Key Techniques
Math problems test number theory, combinatorics, and modular arithmetic. Common tools: GCD/LCM (Euclidean algorithm), prime sieve, modular inverse (Fermat's little theorem), digit manipulation, and bit tricks. Overflow is a key concern in C# — use long when products may exceed 2³¹.
Combinatorial game theory analyzes who wins under optimal play. Sprague-Grundy theorem assigns "nim-values" to game states. For simple games, look for patterns in small cases. Minimax (with alpha-beta pruning) solves general two-player zero-sum games.
String problems range from simple character counting to complex pattern matching. Common approaches include two pointers, sliding window, prefix hashing, and the KMP algorithm. In C#, strings are immutable — use StringBuilder for efficient concatenation inside loops.
// Approach: Count vowels; Alice wins if count is odd or nonzero (she can always take advantage).
// Time: O(n) Space: O(1)
public class Solution
{
public bool DoesAliceWin(string s)
{
// Define vowels as a constant string
string vowels = "aeiou";
// Iterate through each character in the input string
for (int i = 0; i < s.Length; i++)
{
char currentChar = s[i];
// Check if the current character is a vowel
if (vowels.IndexOf(currentChar) != -1)
// If a vowel is found, Alice wins
return true;
}
// No vowels found, Alice does not win
return false;
}
}