Valid Anagram

Return whether t is an anagram of s: both strings must contain the same lowercase letters with the same multiplicities, possibly in a different order.

Pattern: Frequency counting with a balance map

• Mental model: every character in s adds one credit, and every character in t spends one credit.
• Invariant: after processing matching positions from both strings, each map value is the net difference seen so far.
• Complexity: counting is O(n) time and O(k) space for k distinct characters; sorting is simpler but costs O(n log n).

Input / output

• Input: s: string, t: string
• Output: boolean

Examples

1. s = "anagram", t = "nagaram" returns true.
2. s = "rat", t = "car" returns false.

Constraints

• 0 <= s.length, t.length <= 100,000
• Both strings contain lowercase English letters only

Follow-up How would full Unicode support change the counting and normalization strategy?