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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

• Java
• C++
• Python
• Go
• TypeScript
• RenderScript

• class Solution {
      public int[] decompressRLElist(int[] nums) {
          int n = 0;
          for (int i = 0; i < nums.length; i += 2) {
              n += nums[i];
          }
          int[] res = new int[n];
          for (int i = 1, k = 0; i < nums.length; i += 2) {
              for (int j = 0; j < nums[i - 1]; ++j) {
                  res[k++] = nums[i];
              }
          }
          return res;
      }
  }
  

• class Solution {
  public:
      vector<int> decompressRLElist(vector<int>& nums) {
          vector<int> res;
          for (int i = 1; i < nums.size(); i += 2) {
              for (int j = 0; j < nums[i - 1]; ++j) {
                  res.push_back(nums[i]);
              }
          }
          return res;
      }
  };
  

• 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
  
  

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

• function decompressRLElist(nums: number[]): number[] {
      let n = nums.length >> 1;
      let ans = [];
      for (let i = 0; i < n; i++) {
          let freq = nums[2 * i],
              val = nums[2 * i + 1];
          ans.push(...new Array(freq).fill(val));
      }
      return ans;
  }
  
  

• impl Solution {
      pub fn decompress_rl_elist(nums: Vec<i32>) -> Vec<i32> {
          let n = nums.len() >> 1;
          let mut ans = Vec::new();
          for i in 0..n {
              for _ in 0..nums[2 * i] {
                  ans.push(nums[2 * i + 1]);
              }
          }
          ans
      }
  }
  
  

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