How do you solve Minimum Amount of Time to Collect Garbage on LeetCode?

Minimum Amount of Time to Collect Garbage (LeetCode #2391) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Only visit houses with garbage to minimize travel time.

What is the time complexity of Minimum Amount of Time to Collect Garbage?

The optimal solution for Minimum Amount of Time to Collect Garbage runs in O(n) time and uses O(1) space. The time complexity is O(n) because we only iterate through the garbage array a limited number of times, making it efficient.

What is the brute force solution for Minimum Amount of Time to Collect Garbage?

The brute force approach for Minimum Amount of Time to Collect Garbage is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves simulating the entire process of garbage collection for each type of garbage truck, visiting every house and calculating the time taken for both travel and collection. This method is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Minimum Amount of Time to Collect Garbage?

Minimum Amount of Time to Collect Garbage uses the following concepts: Array, String, Prefix Sum. The recommended patterns to study are: Prefix Sum, Array.

What are the interview tips for Minimum Amount of Time to Collect Garbage?

Clarify the problem requirements before jumping into coding. Think about edge cases, such as no garbage of a certain type. Explain your thought process clearly while coding.

What are common mistakes when solving Minimum Amount of Time to Collect Garbage?

Not considering the last house for each garbage type. Forgetting to account for travel time correctly.

#2391

Minimum Amount of Time to Collect Garbage

Medium

ArrayStringPrefix SumPrefix SumArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(1)

💡

Intuition

Time O(n)Space O(1)

The optimal approach focuses on minimizing the number of houses visited by each truck. We only need to find the last house for each type of garbage and sum the travel times accordingly, leading to a more efficient solution.

⚙️

Algorithm

3 steps

1Step 1: Initialize total time to the sum of the lengths of all garbage strings (this accounts for collection time).
2Step 2: For each type of garbage ('M', 'P', 'G'), find the last index where that type exists and sum the travel times up to that index.
3Step 3: Return the total time.

solution.py9 lines

1def minTimeToCollectGarbage(garbage, travel):
2    total_time = sum(len(g) for g in garbage)
3    for g in 'MPG':
4        last_index = 0
5        for i in range(len(garbage)):
6            if g in garbage[i]:
7                last_index = i
8        total_time += sum(travel[i] for i in range(last_index))
9    return total_time

ℹ

Complexity note: The time complexity is O(n) because we only iterate through the garbage array a limited number of times, making it efficient.

1Only visit houses with garbage to minimize travel time.
2Collect all garbage types in a single pass to optimize performance.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.