Valid Anagram - Implementation

Here's the solution using one map:

function isAnagram(s, t)
    if length of s != length of t
        return false

    freq := empty hash map

    for each char in s
        freq[char] := freq[char] + 1  // default 0

    for each char in t
        if char not in freq or freq[char] = 0
            return false
        freq[char] := freq[char] - 1

    return true

Time: $O(n)$. Space: $O(k)$ where $k$ is the alphabet size.