Minimum Number of Food Buckets to Feed the Hamsters

Minimum Number of Food Buckets to Feed the Hamsters

1. What is this problem about?

The Minimum Number of Food Buckets to Feed the Hamsters coding problem features a street with hamsters ('H') and empty spaces ('.'). You want to place the minimum number of food buckets such that every hamster has access to at least one. A hamster can eat from a bucket if it is placed in an adjacent empty space (either to its left or right). If a hamster cannot be fed, return -1.

2. Why is this asked in interviews?

This question is frequently used by Microsoft and Sprinklr to test Greedy optimization. It requires the candidate to make the "best" local decision that benefits the most hamsters. It’s a classic example of how a simple linear scan with a specific priority can solve a problem that might otherwise look like a complex search.

3. Algorithmic pattern used

The problem falls under the String, Greedy, Dynamic Programming interview pattern. The greedy strategy is:

1. Iterate through the street.
2. If you see a hamster that is already fed (by a bucket placed to its left), skip it.
3. If not, try to place a bucket to its right (index + 1). This is optimal because it could potentially feed another hamster at index + 2.
4. If you can't place it to the right, try to place it to its left (index - 1).
5. If both are impossible, the hamster can't be fed—return -1.

4. Example explanation

Street: "H.H.H"

1. First 'H' at index 0. Try right (index 1). It's empty. Place bucket. Street becomes: "HB H . H" (B = bucket)
2. 'H' at index 2. It is adjacent to the bucket at index 1. Already fed!
3. 'H' at index 4. Try right? No space. Try left (index 3). It's empty. Place bucket. Total buckets: 2.

5. Common mistakes candidates make

A common mistake is placing buckets arbitrarily or always placing them on the left first. This fails to account for the "shared" bucket potential on the right. Another error is not checking boundary conditions (beginning or end of the string) when looking for empty spaces. Forgetting to mark a hamster as "fed" when a future bucket is placed can also lead to double-counting.

6. Interview preparation tip

Greedy problems often rely on "looking ahead." By placing a bucket on the right side of a hamster, you are maximizing the chance that the next hamster can also use it. Practice identifying these "highest impact" placements in similar interval or coverage problems.