algoadvance

You are given a list nums where each pair of elements in the list represent [frequency, value] sequence. Your task is to return the decompressed version of the list where each value appears frequency times consecutively in the list.

Example:

• Input: nums = [1,2,3,4]
• Output: [2,4,4,4]

Clarifying Questions

1. Size Constraints: What is the maximum length of the input list nums?
   • The length of nums is guaranteed to be even, and it’s between 2 and 100.
2. Element Constraints: What are the possible values for frequency and value?
   • Frequency values are between 1 and 100.
   • Value elements are between 1 and 100.

Strategy

1. Initialize an empty list:
   • This will be used to store the decompressed values.
2. Iterate through the nums list:
   • Loop through the list in steps of 2.
   • For each pair of elements, extract the frequency and value.
3. Extend the list:
   • Use the extend method to add the value repeated frequency times to the resulting list.
4. Return the decompressed list:
   • After processing all pairs, return the resulting list.

Time Complexity

• Time Complexity: Every pair is processed once, and for each frequency f, we add f elements to the result. In the worst case, where the total number of elements added is proportional to the sum of frequencies, time complexity is O(n), where n is the sum of all frequencies in the input list.
• Space Complexity: The extra space used is O(n), where n is the length of the output list.

Code

def decompressRLElist(nums):
    decompressed_list = []
    for i in range(0, len(nums), 2):
        frequency = nums[i]
        value = nums[i + 1]
        decompressed_list.extend([value] * frequency)
    return decompressed_list

Example Run

Let’s test the implementation with one of the provided examples:

Example 1:

• Input: nums = [1, 2, 3, 4]
• Output: [2, 4, 4, 4]

Explanation:

• The first pair is [1, 2]: This means 2 appears 1 time.
• The second pair is [3, 4]: This means 4 appears 3 times.

So, the decompressed list is [2, 4, 4, 4].

Using the provided implementation, this would effectively solve the given problem.

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