LeetCode-in-Java

1313. Decompress Run-Length Encoded List

Easy

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

Solution

public class Solution {
    public int[] decompressRLElist(int[] nums) {
        int len = 0;
        for (int i = 0; i < nums.length; i += 2) {
            len += nums[i];
        }
        int[] ans = new int[len];
        int index = 0;
        for (int i = 0; i < nums.length; i += 2) {
            int j = nums[i];
            while (j > 0) {
                ans[index] = nums[i + 1];
                index++;
                j--;
            }
        }
        return ans;
    }
}

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