[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

这道题给了一个压缩后的数组，压缩的方法是将相同连续的数字的个数和其本身组成个数对儿，放到压缩数组中，以此类推。现在让我们解压缩成原来的数组，没啥太大的难度，就是每次取出两个数字，前一个数字是次数，后一个是数字本身，用一个 for 循环，就可以生成给定次数个数字，用这种方法就可以解压缩出原数组了，参见代码如下：

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

Github 同步地址:

#1313

类似题目：

String Compression

参考资料：

https://leetcode.com/problems/decompress-run-length-encoded-list/

https://leetcode.com/problems/decompress-run-length-encoded-list/discuss/521777/Java-100-time

https://leetcode.com/problems/decompress-run-length-encoded-list/discuss/477498/C%2B%2B-vector.insert(end-a-b)

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