3541. Find Most Frequent Vowel and Consonant
Approach
Count vowel and consonant frequencies; return max-freq vowel + max-freq consonant.
Key Techniques
Hash tables provide O(1) average-case lookup, insert, and delete. They are the go-to tool for counting frequencies, detecting complements (Two Sum pattern), and caching seen values. In C#, use Dictionary<K,V> for maps and HashSet<T> for membership checks.
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.
Counting problems enumerate valid configurations without explicitly generating them. Techniques: combinatorics (nCr), inclusion-exclusion, digit DP, and contribution of each element. In C#, use long to avoid overflow when multiplying counts.
// Approach: Count vowel and consonant frequencies; return max-freq vowel + max-freq consonant.
// Time: O(n) Space: O(26)
public class Solution
{
public int MaxFreqSum(string s)
{
// Array to store frequency count of each letter (a-z)
int[] frequencyCount = new int[26];
// Count the frequency of each character in the string
foreach (char character in s)
frequencyCount[character - 'a']++;
// Variables to track maximum frequency among vowels and consonants
int maxVowelFrequency = 0;
int maxConsonantFrequency = 0;
// Iterate through the frequency array to find max frequencies
for (int i = 0; i < frequencyCount.Length; i++)
{
char currentChar = (char)(i + 'a');
// Check if current character is a vowel
if (currentChar == 'a' || currentChar == 'e' || currentChar == 'i' ||
currentChar == 'o' || currentChar == 'u')
// Update maximum vowel frequency if current is greater
maxVowelFrequency = Math.Max(maxVowelFrequency, frequencyCount[i]);
else
// Update maximum consonant frequency if current is greater
maxConsonantFrequency = Math.Max(maxConsonantFrequency, frequencyCount[i]);
}
// Return the sum of maximum vowel frequency and maximum consonant frequency
return maxVowelFrequency + maxConsonantFrequency;
}
}