#3248

Easy

LeetCode Problem Workspace

Snake in Matrix

Solve the Snake in Matrix problem by simulating the snake's movement in a grid based on a series of directional commands.

array string simulation

Problem Statement

In an n x n matrix, a snake starts at the top-left cell (0, 0) and follows a sequence of commands. Each command can move the snake in one of four directions: UP, DOWN, LEFT, or RIGHT. The snake's current position in the matrix is determined by its row and column index, which is represented by the formula grid[i][j] = (i * n) + j. Given an integer n for the grid size and a list of commands, you must calculate the final position of the snake after executing all the commands.

The commands will not cause the snake to move out of bounds, and the movement will be limited to the grid size. After processing all the commands, return the final position of the snake in the grid as a single integer.

Examples

Example 1

Input: n = 2, commands = ["RIGHT","DOWN"]

Output: 3

Example 2

Input: n = 3, commands = ["DOWN","RIGHT","UP"]

Output: 1

Constraints

2 <= n <= 10
1 <= commands.length <= 100
commands consists only of "UP", "RIGHT", "DOWN", and "LEFT".
The input is generated such the snake will not move outside of the boundaries.

Solution Approach

Simulating the Movement

Track the snake's position by maintaining variables for its current row and column. Iterate over each command, adjusting the row or column accordingly. This simulation directly updates the position after each movement, taking care to ensure that the snake doesn't move out of the grid boundaries.

Optimized Grid Calculation

Given the matrix structure, calculate the final position directly using the row and column indices. By applying the formula grid[i][j] = (i * n) + j, you can return the final position in the grid as a number after all movements have been executed.

Handling Edge Cases

Ensure that edge cases, like moving in a sequence of commands that lead to the edge of the grid or following a series of opposite directions, are handled correctly. These cases may require validating the updated position after each command to avoid invalid calculations.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

The time complexity of this problem is O(m), where m is the number of commands. Each command only requires a constant amount of work to update the position. The space complexity is O(1) as the solution only uses a constant amount of extra space for the row and column indices.

What Interviewers Usually Probe

The candidate can efficiently simulate the movement of the snake using simple row and column updates.
The candidate understands the need to update indices based on the given commands and matrix dimensions.
The candidate handles edge cases, such as boundary movements and command sequences, effectively.

Common Pitfalls or Variants

Common pitfalls

Failing to correctly simulate the movement based on the command sequence, especially when alternating between opposite directions.
Not updating the snake's position correctly after each command, leading to an incorrect final position.
Misunderstanding the matrix indexing formula and incorrectly calculating the final position in the grid.

Follow-up variants

Changing the grid size n to be larger, which may involve handling a more extensive range of commands.
Implementing the problem with additional constraints, such as limiting the number of directions or varying grid sizes dynamically.
Simulating the movement in a larger matrix with more complex or dynamic command inputs, testing the solution's robustness.

FAQ

What is the key approach to solving Snake in Matrix?

The key approach is to simulate the snake's movement by updating the row and column position based on each command and then calculating the final position in the grid.

How do I handle boundary movements in the Snake in Matrix problem?

The problem guarantees that the snake will stay within the grid boundaries, so the focus should be on correctly updating the row and column for each command.

How does GhostInterview help with solving Snake in Matrix?

GhostInterview guides you in simulating the snake's movement efficiently, ensuring each command is processed correctly and edge cases are handled.

What is the time complexity of the Snake in Matrix problem?

The time complexity is O(m), where m is the number of commands, since each command requires constant time to process.

What should I focus on when solving Snake in Matrix?

Focus on simulating the movement of the snake and correctly updating its position based on the commands, ensuring the final position is accurately calculated.

terminal

Solution

Solution 1: Simulation

We can use two variables $x$ and $y$ to represent the position of the snake. Initially, $x = y = 0$. Then, we traverse $\textit{commands}$ and update the values of $x$ and $y$ based on the current command. Finally, we return $x \times n + y$.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

class Solution:
    def finalPositionOfSnake(self, n: int, commands: List[str]) -> int:
        x = y = 0
        for c in commands:
            match c[0]:
                case "U":
                    x -= 1
                case "D":
                    x += 1
                case "L":
                    y -= 1
                case "R":
                    y += 1
        return x * n + y

Continue Practicing

#3522 calculate score after performing instructions #2744 find maximum number of string pairs #3242 design neighbor sum service