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What difficulty level is this coding question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Roblox.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Roblox during technical interviews.

Can the character reach the destination?

Quick Overview

This question evaluates understanding of graph traversal and reachability in grid-based pathfinding, covering skills such as modeling a 2D grid as a graph, handling obstacles and boundary conditions, and algorithmic traversal strategies.

Can the character reach the destination?

Company: Roblox

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

You control a character starting at a start cell and want to reach a target cell in a 2D grid. Some cells are blocked by obstacles and cannot be entered. Given a grid of size m x n containing: - 'S' = start (exactly one) - 'T' = target (exactly one) - '#' = obstacle (cannot step on) - '.' = free cell The character may move one step at a time in 4 directions (up, down, left, right) and must stay within the grid. Return whether it is possible to reach 'T' starting from 'S'.

Quick Answer: This question evaluates understanding of graph traversal and reachability in grid-based pathfinding, covering skills such as modeling a 2D grid as a graph, handling obstacles and boundary conditions, and algorithmic traversal strategies.

You are given a 2D grid representing a map. There is exactly one start cell 'S' and exactly one target cell 'T'. Some cells contain obstacles '#', which cannot be entered, and free cells are marked with '.'. The character starts at 'S' and can move one step at a time in four directions: up, down, left, and right. The character must stay inside the grid and cannot move onto obstacle cells. Return whether it is possible to reach 'T' starting from 'S'.

Constraints

1 <= m, n
All rows in grid have the same length
grid[i][j] is one of 'S', 'T', '#', or '.'
Exactly one 'S' and exactly one 'T' exist in the grid

Examples

Input: (["S..", ".#.", "..T"],)

Expected Output: True

Explanation: A valid path exists around the obstacle: down, down, right, right.

Input: (["S#.", "##.", "..T"],)

Expected Output: False

Explanation: The start cell is completely blocked by obstacles, so no movement is possible.

Input: (["ST"],)

Expected Output: True

Explanation: This single-row edge case is reachable immediately by moving one step to the right.

Input: (["S#..", ".#.#", ".#T#", "...."],)

Expected Output: True

Explanation: Although direct paths are blocked, the character can go around through the bottom row to reach T.

Input: (["S", ".", "#", "T"],)

Expected Output: False

Explanation: In this single-column edge case, the obstacle blocks the only route to the target.

Hints

Think of each open cell as a node in a graph connected to its up, down, left, and right neighbors.
Use BFS or DFS and keep track of visited cells so you do not process the same cell multiple times.

Last updated: May 5, 2026

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