Given a lowercase alphabet string s, determine whether it has all unique characters.

Constraints

0 ≤ n ≤ 100,000 where n is the length of s Example 1 Input s = "abcde" Output true Explanation All characters only occur once Example 2 Input s = "aab" Output false Explanation There's two as Example 3 Input s = "" Output true Explanation All characters occur once (of which there are none)