LeetCode 1313. Decompress Run-Length Encoded List

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

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/**
 * Note: The returned array must be malloced, assume caller calls free().
 */

int* decompressRLElist(int* nums, int numsSize, int* returnSize){
    *returnSize = 0;
    for(int i=0;i<numsSize;i+=2){
        *returnSize += nums[i];
    }
    int* ret = (int*)malloc(sizeof(int)**returnSize);
    int index = 0;
    for(int i=0;i<numsSize;i+=2){
        for(int j=0;j<nums[i];++j){
            ret[index+j]=nums[i+1];
        }
        index += nums[i];
    }
    return ret;
}


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