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This is a easy difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Boeing.

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This question is commonly asked for Software Engineer candidates at Boeing during technical interviews.

Compute unique-substring length and first unique index

Last updated: Mar 29, 2026

Quick Overview

This question evaluates proficiency in string processing and character-frequency reasoning by combining tasks that measure longest distinct-character substring length and the index of the first non-repeating character.

Boeing

Jan 22, 2026, 12:00 AM

Software Engineer

Technical Screen

Coding & Algorithms

Solve the following two string problems.

Problem 1 — Longest substring with all distinct characters

Given a string s, find the length of the longest contiguous substring that contains no repeated characters.

Input: s (ASCII or Unicode string)
Output: an integer length
Constraints (typical): 0 ≤ |s| ≤ 10^5

Example:

s = "abcabcbb" → output 3 (substring could be "abc" )

Problem 2 — First unique character

Given a string s, return the index (0-based) of the first character that appears exactly once in the entire string. If no such character exists, return -1.

Input: s
Output: integer index or -1
Constraints (typical): 0 ≤ |s| ≤ 10^5

Example:

s = "leetcode" → output 0
s = "aabb" → output -1