Given a string s, return a new string containing each character only the first time it appears, preserving…

Question

Given a string s, return a new string containing each character only the first time it appears, preserving the original left-to-right order. For example 'banana' becomes 'ban'. The string may be empty and may contain any printable characters.

Prep Room · Answer

**Intuition** We want the first appearance of each character, in original order. A set remembers which characters we've already emitted, so we can skip repeats…

First occurrence characters