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
Solution: Hashtable + Sorting
Use a hashtable to track the frequency of each number.
Time complexity: O(nlogn)
Space complexity: O(n)
C++
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class Solution { public: vector<int> frequencySort(vector<int>& nums) { unordered_map<int, int> freq; for (int x : nums) ++freq[x]; sort(begin(nums), end(nums), [&](int a, int b) { if (freq[a] != freq[b]) return freq[a] < freq[b]; return a > b; }); return nums; } }; |
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