Given a non-empty array of integers, return the k most frequent elements.
For example,
Given [1,1,1,2,2,3] and k = 2, return [1,2].
Note:
- You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
- Your algorithm‘s time complexity must be better than O(n log n), where n is the array‘s size.
1 public class Solution { 2 public IList<int> TopKFrequent(int[] nums, int k) { 3 var dict = new Dictionary<int, int>(); 4 5 foreach (var n in nums) 6 { 7 if (!dict.ContainsKey(n)) 8 { 9 dict[n] = 0; 10 } 11 12 dict[n]++; 13 } 14 15 var freq = new List<int>[nums.Length + 1]; 16 17 foreach (var kv in dict) 18 { 19 if (freq[kv.Value] == null) 20 { 21 freq[kv.Value] = new List<int>(); 22 } 23 24 freq[kv.Value].Add(kv.Key); 25 } 26 27 var result = new List<int>(); 28 for (int i = nums.Length; i >= 0; i--) 29 { 30 if (freq[i] != null) 31 { 32 foreach (var v in freq[i]) 33 { 34 result.Add(v); 35 if (result.Count >= k) return result; 36 } 37 } 38 } 39 40 return result; 41 } 42 }