Longest Substring with At Most Two Distinct Characters

Given a string s, your task is to find the longest contiguous substring that contains at most \(2\) distinct characters. This problem can be solved optimally using a sliding window (two pointers) approach.

Examples:

• For s = "eceba", the longest substring is "ece".
• For s = "ccaabbb", the longest substring is "aabbb".

Note: If there are multiple substrings with the maximum length, output the one which appears first.

inputFormat

The input consists of a single line containing the string s.

outputFormat

Print the longest contiguous substring of s that contains at most 2 distinct characters.

eceba

ece