Used by thousands of developers who passed their interviews
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.
Phantom Code generates complete solutions and debugging hints that you can use while explaining your approach, so you stay calm and in control.
undetectable
real-time
works on major platforms
Start Free for WindowsMedium#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.
ArrayTwo PointersBinary SearchBit Manipulation
Phantom Code will help you solve this problem in real-time during your interview
Get instant solutions, explanations, and code generation
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
Related Topics
ArrayTwo PointersBinary SearchBit Manipulation
How Phantom Code Helps
Get real-time assistance for Find the Duplicate Number problems during coding interviews. Phantom Code 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 Phantom Code Helps with LeetCode Problems
Reinforce undetectability, platform compatibility, and real-time assistance to remove any doubt.
1000+
developers use Phantom Code
and growing every day
95%
success rate
of users pass their interviews
100%
undetectable
native desktop architecture
Real-time
assistance
instant solutions during interviews
See Phantom Code in Action
Watch how Phantom Code helps solve LeetCode problems during live interviews
Start Interview
⌘I
Online Round
⌘O
Hide⌘B
Interview
Listening
Think
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)
Start Over ⌘G
Think & Crack ⌘↵
Undetectability Checklist
Run compatibility test before interviews
Use recommended Zoom version settings
Enable advanced screen capture options
Verify native desktop architecture
Test with screen recording software
Platform Compatibility
Zoom
Supported
Google Meet
Supported
HackerRank
Supported
CodeSignal
Supported
CoderPad
Supported
Teams
Supported
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 Find the Duplicate Number and using Phantom Code during coding interviews.
How does Phantom Code help me solve coding problems like Find the Duplicate Number 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 Find the Duplicate Number?
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 Find the Duplicate Number?
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 Find the Duplicate Number 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 Find the Duplicate Number 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 Find the Duplicate Number 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 Find the Duplicate Number 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 Find the Duplicate Number interviews?
Yes. Phantom Code works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
₹999/month. Zero Detection Cases.
The only AI interview tool with an undetectable desktop overlay, real-time audio listening, and personalized AI responses.