Decompress run length encoded list

Array

86.2% acceptance

Feb 25, 2026

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1325

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.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn decompress_rl_elist(nums: Vec<i32>) -> Vec<i32> {
    let mut res = Vec::new();
    let mut i = 0;
    while i < nums.len() {
      let freq = nums[i] as usize;
      let val = nums[i + 1];
      for _ in 0..freq {
        res.push(val);
      }
      i += 2;
    }
    res
  }
}