1313. Decompress Run-Length Encoded List

Problem

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

Problem Summary

You are given an integer list nums compressed with run-length encoding. Consider each adjacent pair of elements [freq, val] = [nums[2i], nums[2i+1]] (where i >= 0 ). Each pair represents that the decompressed sublist contains freq elements with value val. You need to concatenate all sublists from left to right to generate the decompressed list. Return the decompressed list.

Solution Ideas

• Given an array with encoded lengths, we need to decompress this array.
• Easy problem. According to the requirements, starting from index 0, the element at each even index is the number of repetitions of the element at the next index, so append that element several times. Finally, output the decompressed array.

Code

package leetcode

func decompressRLElist(nums []int) []int {
	res := []int{}
	for i := 0; i < len(nums); i += 2 {
		for j := 0; j < nums[i]; j++ {
			res = append(res, nums[i+1])
		}
	}
	return res
}