# [LeetCode]#1313. Decompress Run-Length Encoded List

**Environment: Python 3.7**

**Key technique:** extend function

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`

**Analysis:**

The odd means frequent and even means number. Use extend function to solve it as below.

**Solution:**

`class Solution:`

def decompressRLElist(self, nums):

ans=[]

l=len(nums)

for i in range(0,l,2):

ans.extend(nums[i]*[nums[i+1]])

return ans

**Submitted result:**

**Reference:**