1313-decompress-run-length-encoded-list.py

"""
Problem Link: 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
"""
class Solution:
    def decompressRLElist(self, nums: List[int]) -> List[int]:
        res = []
        for i in range(1, len(nums), 2):
          res.extend([nums[i]]*nums[i-1])
        return res