LeetCode 1313. Decompress Run-Length Encoded List

Description

https://leetcode.com/problems/decompress-run-length-encoded-list/

We are given a list nums of integers representing a list compressed with run-length encoding.

Consider each adjacent pair of elements [freq, val] = [nums[2*i], nums[2*i+1]] (with i >= 0).  For each such pair, there are freq elements with value val concatenated in a sublist. Concatenate all the sublists from left to right to generate the decompressed list.

Return the decompressed list.

Example 1:

Input: nums = [1,2,3,4]
Output: [2,4,4,4]
Explanation: The first pair [1,2] means we have freq = 1 and val = 2 so we generate the array [2].
The second pair [3,4] means we have freq = 3 and val = 4 so we generate [4,4,4].
At the end the concatenation [2] + [4,4,4] is [2,4,4,4].

Example 2:

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

Constraints:

  • 2 <= nums.length <= 100
  • nums.length % 2 == 0
  • 1 <= nums[i] <= 100

Explanation

Step by 2 each time to add pairs.

Python Solution

class Solution:
    def decompressRLElist(self, nums: List[int]) -> List[int]:
        results = []
                
        for i in range(1, len(nums), 2):
            freq = nums[i - 1]
            value = nums[i]
            
            for j in range(freq):
                results.append(value)
        
        return results
  • Time Complexity: O(logN)
  • Space Complexity: O(N)

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