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HomeLeetCode ProblemsConstruct the Lexicographically Largest Valid Sequence
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How to Solve Construct the Lexicographically Largest Valid Sequence Problem

Master the Construct the Lexicographically Largest Valid Sequence LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.

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Medium#1718
LeetCode Problem

Construct the Lexicographically Largest Valid Sequence

Given an integer n, find a sequence with elements in the range [1, n] that satisfies all of the following: The distance between two numbers on the sequence, a[i] and a[j], is the absolute difference of their indices, |j - i|. Return the lexicographically largest sequence. It is guaranteed that under the given constraints, there is always a solution. A sequence a is lexicographically larger than a sequence b (of the same length) if in the first position where a and b differ, sequence a has a number greater than the corresponding number in b. For example, [0,1,9,0] is lexicographically larger than [0,1,5,6] because the first position they differ is at the third number, and 9 is greater than 5.

ArrayBacktracking

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Problem Breakdown

Understanding the Construct the Lexicographically Largest Valid Sequence Problem

Let's break down this LeetCode problem and understand what makes it challenging in interview settings.

Problem Statement

Given an integer n, find a sequence with elements in the range [1, n] that satisfies all of the following: The distance between two numbers on the sequence, a[i] and a[j], is the absolute difference of their indices, |j - i|. Return the lexicographically largest sequence. It is guaranteed that under the given constraints, there is always a solution. A sequence a is lexicographically larger than a sequence b (of the same length) if in the first position where a and b differ, sequence a has a number greater than the corresponding number in b. For example, [0,1,9,0] is lexicographically larger than [0,1,5,6] because the first position they differ is at the third number, and 9 is greater than 5.

MediumProblem #1718
LeetCode

Construct the Lexicographically Largest Valid Sequence

Related Topics

ArrayBacktracking

How Phantom Code Helps

Get real-time assistance for Construct the Lexicographically Largest Valid Sequence problems during coding interviews. Phantom Code provides instant solutions and explanations.

Examples

# Example 1

Input
n = 3
Output
[3,1,2,3,2]

# Example 2

Input
n = 5
Output
[5,3,1,4,3,5,2,4,2]

Constraints

1 <= n <= 20

How Phantom Code Helps with LeetCode Problems

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Solve Construct the Lexicographically Largest Valid Sequence — Given an integer n, find a sequence with elements in the range [1, n] that satis...

Here's the optimal approach using Array:

def solve(input):
# Optimal O(n) solution
return result

Time: O(n)  |  Space: O(n)

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Undetectability Checklist

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Platform Compatibility

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User results and traction

Thousands of developers use Phantom Code. Social proof signals that this approach helps real candidates land offers across a range of companies.

Undetectability and technical details

Our native desktop architecture avoids common detection vectors used by browser extensions. We provide a clear checklist so you can run basic checks and confirm the app will be invisible.

Platform compatibility and limitations

We work with Zoom, HackerRank, CodeSignal, CoderPad and other web-based platforms. Check the compatibility note and request a browser link if a specific desktop app is unsupported.

Frequently Asked Questions

Common questions about solving Construct the Lexicographically Largest Valid Sequence and using Phantom Code during coding interviews.

How does Phantom Code help me solve coding problems like Construct the Lexicographically Largest Valid Sequence during interviews?
Phantom Code generates complete solutions instantly with proper complexity analysis, letting you focus on explaining your approach and demonstrating problem-solving skills rather than getting stuck on implementation details during high-pressure situations.
What if the interviewer asks follow-up questions or modifications to problems like Construct the Lexicographically Largest Valid Sequence?
Phantom Code adapts in real-time. Screenshot the modified problem or use audio mode to capture the interviewer's follow-up, and get an updated solution within seconds — including edge cases and optimizations.
Can Phantom Code help me communicate my solution for problems like Construct the Lexicographically Largest Valid Sequence?
Yes. Phantom Code provides step-by-step approach explanations with 3 progressive thoughts, so you can walk through your solution naturally. It also provides time and space complexity analysis to discuss trade-offs.
How does Phantom Code assist with different programming languages for Construct the Lexicographically Largest Valid Sequence type problems?
Phantom Code supports 11 programming languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set your preferred language and get idiomatic solutions.
What coding mistakes does Phantom Code help me avoid during Construct the Lexicographically Largest Valid Sequence interviews?
Phantom Code catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
Is Phantom Code detectable when solving problems like Construct the Lexicographically Largest Valid Sequence during live interviews?
No. Phantom Code runs as an invisible desktop overlay that doesn't appear in screen shares, recordings, or proctoring software. It works with Zoom, HackerRank, CodeSignal, CoderPad, and all major platforms.
How does Phantom Code help when I'm struggling with Construct the Lexicographically Largest Valid Sequence style questions under pressure?
The AI provides structured guidance: first the approach (what algorithm/data structure to use and why), then the implementation with clean code, and finally complexity analysis. This helps you think clearly even under pressure.
Does Phantom Code work for the coding platforms used in Construct the Lexicographically Largest Valid Sequence interviews?
Yes. Phantom Code works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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