LeetCode 2069 | Walking Robot Simulation II | Java | Medium | Design & Simulation | CodeByTushu
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In today’s video, we solve LeetCode 2069 — Walking Robot Simulation II using Design and Simulation in Java.
In this problem, we need to design a robot that navigates along the outer perimeter of a grid of width w and height h. The robot starts at cell (0, 0) facing East and moves in a counter-clockwise loop along the boundary. When moving forward reaches the boundary, the robot turns 90 degrees counter-clockwise before retrying the step. Because the robot never visits interior cells, its entire trajectory is confined to a 1D loop of perimeter length 2 * (w + h) - 4.
Instead of simulating step-by-step movement which would result in Time Limit Exceeded when moving up to 10^5 steps repeatedly, we precalculate the ordered boundary coordinates and their corresponding orientations. By tracking the total steps modulo the perimeter length, every move, position query, and direction query can be executed in O(1) time. We also account for the crucial edge case where the robot is at (0, 0) before any move (facing East) versus arriving at (0, 0) after full perimeter cycles (facing South).
🔥 Problem Highlights
✅ Boundary Trajectory Mapping: Confining movements to the perimeter loop of length 2 * (w + h) - 4
✅ O(1) Step Processing: Using modular arithmetic on cumulative steps to eliminate repetitive looping
✅ Precomputed State Arrays: Instant coordinate and direction retrieval via position index
✅ Origin State Edge Case: Distinguishing initial rest facing East from post-movement arrival facing South
✅ Constant Time Complexity: All queries execute in O(1) time after O(width + height) precomputation
✅ Memory Efficiency: O(width + height) auxiliary space to store perimeter states
⏱️ TIMESTAMPS
00:00 Intro & Daily Challenge Kickoff (Streak 98 Days)
01:32 Problem Understanding & Boundary Cycle Dynamics
03:32 Key Insights: Perimeter Modulo Math & Origin Nuance
05:36 Optimal Precomputed Perimeter Array Traversal
07:27 Clean Java Solution Walkthrough Line by Line
08:44 Test Cases Dry Run & Benchmark Verification (61 ms, Beats 95.8%)
10:39 Time Complexity Analysis (O(W+H) Init, O(1) Operations)
11:48 Space Complexity Analysis (O(W+H) Boundary Arrays)
12:39 Day 7 Wrap-up & Channel Resources
📂 Problem Folder & Detailed Documentation:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/tree/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II
☕ Java Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/Solution.java
🐍 Python Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.py
⚡ C++ Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.cpp
🌐 JavaScript Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.js
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💬 Question of the Day
Why does the robot at cell (0, 0) face "South" instead of "East" after taking a positive number of steps that ends up at (0, 0)?
1️⃣ Because the robot always rotates 180 degrees at (0, 0)
2️⃣ It entered (0, 0) by moving down from (0, 1), so its direction is South
3️⃣ The problem specification arbitrarily resets direction to South
4️⃣ Modular arithmetic causes an off-by-one direction shift
#LeetCode2069 #LeetCode #WalkingRobotSimulationII #Java #JavaDSA #Design #Simulation #DSA #CodingInterview #ProblemSolving #LeetCodeMedium #DailyLeetCode #JavaProgramming #CodeByTushu
👇 Comment the answer below! 🔥 Close description
In today’s video, we solve LeetCode 2069 — Walking Robot Simulation II using Design and Simulation in Java.
In this problem, we need to design a robot that navigates along the outer perimeter of a grid of width w and height h. The robot starts at cell (0, 0) facing East and moves in a counter-clockwise loop along the boundary. When moving forward reaches the boundary, the robot turns 90 degrees counter-clockwise before retrying the step. Because the robot never visits interior cells, its entire trajectory is confined to a 1D loop of perimeter length 2 * (w + h) - 4.
Instead of simulating step-by-step movement which would result in Time Limit Exceeded when moving up to 10^5 steps repeatedly, we precalculate the ordered boundary coordinates and their corresponding orientations. By tracking the total steps modulo the perimeter length, every move, position query, and direction query can be executed in O(1) time. We also account for the crucial edge case where the robot is at (0, 0) before any move (facing East) versus arriving at (0, 0) after full perimeter cycles (facing South).
🔥 Problem Highlights
✅ Boundary Trajectory Mapping: Confining movements to the perimeter loop of length 2 * (w + h) - 4
✅ O(1) Step Processing: Using modular arithmetic on cumulative steps to eliminate repetitive looping
✅ Precomputed State Arrays: Instant coordinate and direction retrieval via position index
✅ Origin State Edge Case: Distinguishing initial rest facing East from post-movement arrival facing South
✅ Constant Time Complexity: All queries execute in O(1) time after O(width + height) precomputation
✅ Memory Efficiency: O(width + height) auxiliary space to store perimeter states
⏱️ TIMESTAMPS
00:00 Intro & Daily Challenge Kickoff (Streak 98 Days)
01:32 Problem Understanding & Boundary Cycle Dynamics
03:32 Key Insights: Perimeter Modulo Math & Origin Nuance
05:36 Optimal Precomputed Perimeter Array Traversal
07:27 Clean Java Solution Walkthrough Line by Line
08:44 Test Cases Dry Run & Benchmark Verification (61 ms, Beats 95.8%)
10:39 Time Complexity Analysis (O(W+H) Init, O(1) Operations)
11:48 Space Complexity Analysis (O(W+H) Boundary Arrays)
12:39 Day 7 Wrap-up & Channel Resources
📂 Problem Folder & Detailed Documentation:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/tree/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II
☕ Java Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/Solution.java
🐍 Python Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.py
⚡ C++ Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.cpp
🌐 JavaScript Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/April/07-April/2069-Walking-Robot-Simulation-II/solution.js
🔗 LeetCode Source Code
📌 Admin type the link
🌐 All LeetCode Solutions
📌 https://codebytushu.com/Leetcode/
📱 Join CodeByTushu on WhatsApp
Get coding updates, LeetCode solutions, daily questions and more.
https://whatsapp.com/channel/0029Vb8k5mCDeON2Xwlkxe40
❤️ Donate
📌 https://codebytushu.com/Leetcode/donate.php
🔥 Perfect For
LeetCode Medium Problems
Java DSA Preparation
Design and State Machine
Boundary Simulation & Modular Arithmetic
Matrix & Grid Traversal
Time Complexity Optimization
Coding Interview Preparation
Problem Solving
🌐 Follow CodeByTushu
▶️ YouTube: https://www.youtube.com/@codebytushu
📸 Instagram: https://instagram.com/codebytushu/
💼 LinkedIn: https://www.linkedin.com/company/codebytushu/
🌍 Website: https://codebytushu.com
🐙 GitHub: https://github.com/CodeByTushu
❤️ Don’t Forget To
👍 Like | 💬 Comment | 🔔 Subscribe
💬 Question of the Day
Why does the robot at cell (0, 0) face "South" instead of "East" after taking a positive number of steps that ends up at (0, 0)?
1️⃣ Because the robot always rotates 180 degrees at (0, 0)
2️⃣ It entered (0, 0) by moving down from (0, 1), so its direction is South
3️⃣ The problem specification arbitrarily resets direction to South
4️⃣ Modular arithmetic causes an off-by-one direction shift
#LeetCode2069 #LeetCode #WalkingRobotSimulationII #Java #JavaDSA #Design #Simulation #DSA #CodingInterview #ProblemSolving #LeetCodeMedium #DailyLeetCode #JavaProgramming #CodeByTushu
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