1313. Decompress Run-Length Encoded List

问题：

给定一个数组，相邻两两元素构成编码，第一个元素代表出现次数，第二个元素代表出现的元素。

求编码前的原数组。

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

　　

解法：

遍历编码数组，每次遍历取出一个编码对，两个元素 i+=2。

再循环出现次数freq次，将元素nums[i+1] push_back到结果中。

代码参考：

class Solution {
public:
    vector<int> decompressRLElist(vector<int>& nums) {
        vector<int> res;
        for(int i=0; i+1<nums.size(); i+=2){
            for(int freq=nums[i];freq>0;freq--){
                res.push_back(nums[i+1]);
            }
        }
        return res;
    }
};