Cut Off Trees for Golf Event
What is this problem about?
The Cut Off Trees for Golf Event interview question is a complex matrix traversal problem. You are given a 2D forest where 0 is an obstacle, 1 is a walk-through path, and values > 1 represent trees with specific heights. You must cut down all the trees in order from shortest to tallest. You start at (0,0). The goal is to find the minimum number of steps to cut all trees. If you can't reach a tree, return -1. This Cut Off Trees for Golf Event coding problem is a multi-stage shortest-path challenge.
Why is this asked in interviews?
Amazon and Flipkart ask this to test your mastery of graph algorithms. It’s not just a single Breadth-First Search (BFS); it’s a sequence of BFS calls. It evaluates how you manage coordinates, how you handle obstacles, and whether you can efficiently sort and process targets in a grid.
Algorithmic pattern used
This utilizes the Array, Matrix, Breadth-First Search, Heap (Priority Queue) interview pattern.
- Sort: Collect all trees and sort them by height.
- Iterate: For each pair of consecutive trees (starting from the origin to the shortest, then shortest to next shortest...), calculate the shortest distance.
- Shortest Path: Use BFS to find the minimum steps between two coordinates in a grid with obstacles.
- Accumulate: Sum the steps from each BFS call.
Example explanation
Forest:
[[1, 2, 3], [0, 0, 4], [7, 6, 5]]
- Trees: (0,1):2, (0,2):3, (1,2):4, (2,2):5, (2,1):6, (2,0):7.
- Step 1: (0,0) to (0,1). Distance = 1.
- Step 2: (0,1) to (0,2). Distance = 1.
- Step 3: (0,2) to (1,2). Distance = 1.
Total steps = sum of these individual segments.
Common mistakes candidates make
- Standard BFS Trap: Trying to find a path that cuts trees as it goes. The rule is strict: you must cut them in height order.
- Efficiency: Re-sorting the whole grid or missing the fact that trees are obstacles you can walk through (the only true obstacles are 0s).
- Not Handling -1: Forgetting to immediately return -1 if any single tree in the sequence is unreachable.
Interview preparation tip
Practice the modular BFS. If you can write a clean getDistance(start, end) function, the rest of the problem becomes a simple loop. This "modular" coding style is highly valued in interviews.
