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HomeLeetCode ProblemsRobot Collisions
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How to Solve Robot Collisions Problem

Master the Robot Collisions LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.

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Hard#2751
LeetCode Problem

Robot Collisions

There are n 1-indexed robots, each having a position on a line, health, and movement direction. You are given 0-indexed integer arrays positions, healths, and a string directions (directions[i] is either 'L' for left or 'R' for right). All integers in positions are unique. All robots start moving on the line simultaneously at the same speed in their given directions. If two robots ever share the same position while moving, they will collide. If two robots collide, the robot with lower health is removed from the line, and the health of the other robot decreases by one. The surviving robot continues in the same direction it was going. If both robots have the same health, they are both removed from the line. Your task is to determine the health of the robots that survive the collisions, in the same order that the robots were given, i.e. final health of robot 1 (if survived), final health of robot 2 (if survived), and so on. If there are no survivors, return an empty array. Return an array containing the health of the remaining robots (in the order they were given in the input), after no further collisions can occur. Note: The positions may be unsorted.

ArrayStackSortingSimulation

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Problem Breakdown

Understanding the Robot Collisions Problem

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

Problem Statement

There are n 1-indexed robots, each having a position on a line, health, and movement direction. You are given 0-indexed integer arrays positions, healths, and a string directions (directions[i] is either 'L' for left or 'R' for right). All integers in positions are unique. All robots start moving on the line simultaneously at the same speed in their given directions. If two robots ever share the same position while moving, they will collide. If two robots collide, the robot with lower health is removed from the line, and the health of the other robot decreases by one. The surviving robot continues in the same direction it was going. If both robots have the same health, they are both removed from the line. Your task is to determine the health of the robots that survive the collisions, in the same order that the robots were given, i.e. final health of robot 1 (if survived), final health of robot 2 (if survived), and so on. If there are no survivors, return an empty array. Return an array containing the health of the remaining robots (in the order they were given in the input), after no further collisions can occur. Note: The positions may be unsorted.

HardProblem #2751
LeetCode

Robot Collisions

Related Topics

ArrayStackSortingSimulation

How Phantom Code Helps

Get real-time assistance for Robot Collisions problems during coding interviews. Phantom Code provides instant solutions and explanations.

Examples

# Example 1

Input
positions = [5,4,3,2,1], healths = [2,17,9,15,10], directions = "RRRRR"
Output
[2,17,9,15,10]

# Example 2

Input
positions = [3,5,2,6], healths = [10,10,15,12], directions = "RLRL"
Output
[14]

# Example 3

Input
positions = [1,2,5,6], healths = [10,10,11,11], directions = "RLRL"
Output
[]

Constraints

1 <= positions.length == healths.length == directions.length == n <= 105
1 <= positions[i], healths[i] <= 109
directions[i] == 'L' or directions[i] == 'R'
All values in positions are distinct

How Phantom Code Helps with LeetCode Problems

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See Phantom Code in Action

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Solve Robot Collisions — There are n 1-indexed robots, each having a position on a line, health, and move...

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

Run compatibility test before interviews
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Platform Compatibility

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HackerRank
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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 Robot Collisions and using Phantom Code during coding interviews.

How does Phantom Code help me solve coding problems like Robot Collisions 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 Robot Collisions?
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 Robot Collisions?
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 Robot Collisions 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 Robot Collisions 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 Robot Collisions 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 Robot Collisions 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 Robot Collisions 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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