Hashing in .NET

Why it matters

Hashing is used for frequency counts, duplicate detection, and grouping.

Problems to practice

• Valid Anagram
• Top K Frequent Elements
• First Non-Repeating Character
• Longest Consecutive Sequence
• Subarray Sum Equals K

Example: dictionary count

var frequency = new Dictionary<char, int>();
foreach (var ch in s) {
    if (frequency.ContainsKey(ch)) frequency[ch]++; 
    else frequency[ch] = 1;
}