1636. Sort Array by Increasing Frequency

Given an array of integers nums, sort the array in increasing order based on the frequency of the values. If multiple values have the same frequency, sort them in decreasing order.

Return the sorted array.

 

Example 1:

Input: nums = [1,1,2,2,2,3]
Output: [3,1,1,2,2,2]
Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3.
Example 2:

Input: nums = [2,3,1,3,2]
Output: [1,3,3,2,2]
Explanation: '2' and '3' both have a frequency of 2, so they are sorted in decreasing order.
Example 3:

Input: nums = [-1,1,-6,4,5,-6,1,4,1]
Output: [5,-1,4,4,-6,-6,1,1,1]
 

Constraints:

1 <= nums.length <= 100
-100 <= nums[i] <= 100

这题主要是要使用自定义的排序判断函数。

class SortArrayByIncreasingFrequency : public Solution {
public:
    void Exec() {

    }
    vector<int> frequencySort(vector<int>& nums) {
        if (nums.size() == 1) {
            return nums;
        }
        
        vector<std::pair<int, int>> middle;
        std::sort(nums.begin(),  nums.end());

        int prev = nums[0], count = 1;
        for (int i = 1; i < nums.size(); i++) {
            if (nums[i] == prev) {
                ++count;
            } else {
                middle.push_back(std::make_pair(count, prev));
                count = 1;
            }
            prev = nums[i];
            if (i == nums.size() - 1) {
                middle.push_back(std::make_pair(count, prev));
            }
        }
        std::sort(middle.begin(), middle.end(), [](std::pair<int, int> &a, std::pair<int, int> &b)->bool {
            if (a.first != b.first) {
                return a.first < b.first;
            }
            return a.second > b.second;
        });

        vector<int> res;
        res.reserve(nums.size());
        for (auto &v : middle) {
            for (int i = 0; i < v.first; i++) {
                res.push_back(v.second);
            }
        }
        return res;
    }
};