1313. Decompress Run-Length Encoded List
Description
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
Solutions
Solution 1: Simulation
We can directly simulate the process described in the problem. Traverse the array $\textit{nums}$ from left to right, each time taking out two numbers $\textit{freq}$ and $\textit{val}$, then repeat $\textit{val}$ $\textit{freq}$ times, and add these $\textit{freq}$ $\textit{val}$s to the answer array.
The time complexity is $O(n)$, where $n$ is the length of the array $\textit{nums}$. We only need to traverse the array $\textit{nums}$ once. Ignoring the space consumption of the answer array, the space complexity is $O(1)$.
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