Question

1313. Decompress Run-Length Encoded List

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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

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

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;
  }
};

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
  }
}

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* decompressRLElist(int* nums, int numsSize, int* returnSize) {
  int size = 0;
  for (int i = 0; i < numsSize; i += 2) {
    size += nums[i];
  }
  int* ans = malloc(size * sizeof(int));
  for (int i = 0, j = 0; j < numsSize; j += 2) {
    for (int k = 0; k < nums[j]; k++) {
      ans[i++] = nums[j + 1];
    }
  }
  *returnSize = size;
  return ans;
}