tags: leetcode easy Array

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.

Examples

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:

• $2 \leq nums.length \leq 100$
• nums.length % 2 == 0
• $1 \leq nums[i] \leq 100$

Code

int* decompressRLElist(int* nums, int numsSize, int* returnSize) {
    int i, j, count = 0, set = numsSize / 2;
    int* returnArray;
    *returnSize = 0;            // initial size
    for (i = 0; i < set; i++)   // count decompress size
        *returnSize += nums[2 * i];
    // memory allocation decompression space
    returnArray = (int*)malloc(*returnSize * sizeof(int));   
    for (i = 0; i < set; i++)         // double loop for value assign
        for (j = 0; j < nums[2 * i]; j++, count++)
            returnArray[count] = nums[2 * i + 1];
    return returnArray;
}

Complexity

Space	Time
$O(N)$	$O(N)$

Result

• Runtime : 43 ms, 79.43%
• Memory usage : 10.5 MB, 30.86%