Find shortest substring with n unique letters

Q: Find shortest substring with n unique letters

This question evaluates proficiency in string processing, frequency management, and algorithmic optimization for locating constrained contiguous substrings. Commonly asked in the coding & algorithms domain because it reveals how candidates reason about character distinctness and efficiency trade-offs, it targets practical application of algorithmic techniques rather than purely conceptual theory.

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Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

Question

Problem

You are given a string s consisting of lowercase English letters and an integer n (1 ≤ n ≤ 26).

Find the length of the shortest contiguous substring of s that contains exactly n distinct characters.

If no such substring exists, return -1.

Example

Input: s = "aabcbcdbca" , n = 3
One shortest substring with exactly 3 distinct characters is "bca" (length 3), so the output should be 3 .

Find shortest substring with n unique letters

Overview

Problem

Example

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