That solution as written is O(n^3)
This is not an easy problem.
This is not an easy problem.
For each char in the original string there is: * 1 check in hashmap (let's assume it was found). This is O(1) * build a new string where we remove that char from the string we are building (string2) and add it to the end. This step may look O(n) initially since we need to find that char in string2 but string2 is capped at 26 characters so it's O(1) * One comparison between the string we are building and the altered version.
How does that make it O(n^3)? I can't see which step inside the initial loop is O(n) or greater.
EDIT: The solution is actually incorrect so this is now semantics.
Interesting use of "semantics".
The question of "how fast does this algorithm run?" is totally independent from the question of "what does this algorithm do?"; the second one is semantic but you're discussing the first here.