Is Number of Spaces Cleaning Robot Cleaned easy or hard?

The problem is rated Medium because the movement rules are simple but detecting cycles requires careful thinking. Recognizing that direction must be part of the state is the key step to avoid infinite loops.

Number of Spaces Cleaning Robot Cleaned Python/Java solution

The typical implementation uses a loop that simulates robot movement while storing visited (row, col, direction) states. Direction arrays handle movement and clockwise rotation. The same logic translates cleanly across Python, Java, C++, and Go with O(m*n) complexity.

How to solve Number of Spaces Cleaning Robot Cleaned in O(n)?

Use simulation with direction arrays and a visited-state set. Track the robot's position and direction, attempt to move forward, and rotate clockwise if blocked. Stop when the same (row, col, direction) state repeats. Since the number of states is bounded by m*n*4, the total runtime becomes O(m*n).

What is the best approach for Number of Spaces Cleaning Robot Cleaned?

The best approach is simulation with visited state tracking. Treat the robot's state as (row, column, direction) and store visited states in a set or boolean array. Once the same state appears again, the robot is in a loop and the simulation stops. This guarantees O(m*n) time because there are only m*n*4 possible states.

Is Number of Spaces Cleaning Robot Cleaned asked at Google/Amazon/Meta?

Grid simulation and robot movement problems appear frequently in interviews at companies like Amazon, Google, and Meta. Variations often test state tracking, cycle detection, and careful implementation of movement rules on a matrix.

What data structure is used in Number of Spaces Cleaning Robot Cleaned?

The solution mainly uses arrays for the grid and direction vectors, plus a set or boolean structure to track visited states. Each state stores row, column, and direction to detect loops during the simulation.

What is the time complexity of Number of Spaces Cleaning Robot Cleaned?

The optimal solution runs in O(m*n) time. Each unique state defined by (row, column, direction) can be processed only once, and there are at most m*n*4 states. The space complexity is also O(m*n) for tracking visited states and cleaned cells.

Description Hints 3 Solution Video 8:33

2061. Number of Spaces Cleaning Robot Cleaned

Medium64.3% acceptance2 companiesPremium elsewhere, free here

A room is represented by a 0-indexed 2D binary matrix room where a 0 represents an empty space and a 1 represents a space with an object. The top left corner of the room will be empty in all test cases.

A cleaning robot starts at the top left corner of the room and is facing right. The robot will continue heading straight until it reaches the edge of the room or it hits an object, after which it will turn 90 degrees clockwise and repeat this process. The starting space and all spaces that the robot visits are cleaned by it.

Return the number of clean spaces in the room if the robot runs indefinitely.

Example 1:

Input: room = [[0,0,0],[1,1,0],[0,0,0]]

Output: 7

Explanation:

The robot cleans the spaces at (0, 0), (0, 1), and (0, 2).
The robot is at the edge of the room, so it turns 90 degrees clockwise and now faces down.
The robot cleans the spaces at (1, 2), and (2, 2).
The robot is at the edge of the room, so it turns 90 degrees clockwise and now faces left.
The robot cleans the spaces at (2, 1), and (2, 0).
The robot has cleaned all 7 empty spaces, so return 7.

Example 2:

Input: room = [[0,1,0],[1,0,0],[0,0,0]]

Output: 1

Explanation:

The robot cleans the space at (0, 0).
The robot hits an object, so it turns 90 degrees clockwise and now faces down.
The robot hits an object, so it turns 90 degrees clockwise and now faces left.
The robot is at the edge of the room, so it turns 90 degrees clockwise and now faces up.
The robot is at the edge of the room, so it turns 90 degrees clockwise and now faces right.
The robot is back at its starting position.
The robot has cleaned 1 space, so return 1.

Example 3:

Input: room = [[0,0,0],[0,0,0],[0,0,0]]

Output: 8

Constraints:

m == room.length
n == room[r].length
1 <= m, n <= 300
room[r][c] is either 0 or 1.
room[0][0] == 0

Asked at 2 companies

Geico Microsoft

Topics

Hints open one at a time

Hint 1

Simulate how the robot moves and keep track of how many spaces it has cleaned so far.

Hint 2

When can we stop the simulation?

Hint 3

When the robot reaches a space that it has already cleaned and is facing the same direction as before, we can stop the simulation.

8:33

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