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How to Solve Find the Duplicate Number Problem
Master the Find the Duplicate Number LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.
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Medium#287
LeetCode ProblemFind the Duplicate Number
Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive. There is only one repeated number in nums, return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space.
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Problem Breakdown
Understanding the Find the Duplicate Number Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive. There is only one repeated number in nums, return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space.
MediumProblem #287
LeetCodeFind the Duplicate Number
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How PhantomCodeAI Helps
Get real-time assistance for Find the Duplicate Number problems during coding interviews. PhantomCodeAI provides instant solutions and explanations.
Examples
# Example 1
Input
nums = [1,3,4,2,2]
Output
2
# Example 2
Input
nums = [3,1,3,4,2]
Output
3
# Example 3
Input
nums = [3,3,3,3,3]
Output
3
Constraints
1 <= n <= 105
nums.length == n + 1
1 <= nums[i] <= n
All the integers in nums appear only once except for precisely one integer which appears two or more times.
How PhantomCodeAI Helps with LeetCode Problems
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Solve Find the Duplicate Number — Given an array of integers nums containing n + 1 integers where each integer is ...
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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Zoom
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HackerRank
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CodeSignal
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CoderPad
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Undetectability and technical details
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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 Find the Duplicate Number and using PhantomCodeAI during coding interviews.
How does PhantomCodeAI help with LeetCode problems during a coding interview?
PhantomCodeAI reads the problem from a screenshot or listens to it via audio, then generates a complete solution with a step-by-step approach and time/space complexity, so you can focus on explaining your reasoning rather than getting stuck on implementation.
Which programming languages does PhantomCodeAI support?
11 languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set a preferred language to get idiomatic solutions.
Does PhantomCodeAI work with HackerRank, CodeSignal, and CoderPad?
Yes — it works alongside LeetCode, HackerRank, CodeSignal, CoderPad, and HackerEarth, plus any browser-based coding environment.
Can PhantomCodeAI handle follow-up questions and modifications?
Yes. Capture the modified problem by screenshot or audio and get an updated solution within seconds, including new edge cases and optimizations.
Is PhantomCodeAI detectable during live interviews?
PhantomCodeAI runs as a native desktop overlay that does not appear in screen shares, recordings, or proctoring software, and works with Zoom, Google Meet, Microsoft Teams, and major coding platforms.
Should I still practice these problems on my own first?
Yes. The most durable preparation is solving problems unaided first, then using AI afterward to review your approach, complexity, and missed edge cases — use it to debrief and learn, not to skip the reps.
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