242-Valid-Anagram.cs

public class Solution {
    public bool IsAnagram(string s, string t) {
        if (s.Length != t.Length) return false;
        if (s == t) return true;

        Dictionary<char, int> sCounts = new Dictionary<char, int>();
        Dictionary<char, int> tCounts = new Dictionary<char, int>();
        
        for (int i = 0; i < s.Length; i++) {
            sCounts[s[i]] = 1 + (sCounts.ContainsKey(s[i]) ? sCounts[s[i]] : 0);
            tCounts[t[i]] = 1 + (tCounts.ContainsKey(t[i]) ? tCounts[t[i]] : 0);
        }

        foreach (char c in sCounts.Keys) {
            int tCount = tCounts.ContainsKey(c) ? tCounts[c] : 0;
            if (sCounts[c] != tCount) return false;
        }
        return true;
    }
}