Merge pull request #225 from hellomrsun/master

Add Top K Frequent Elements C#

Author: jinshendan

July-LeetCoding-Challenge/17-Top-K-Frequent-Elements/Top-K-Frequent-Elements.cs

@@ -0,0 +1,34 @@
+public class Solution {
+    public int[] TopKFrequent(int[] nums, int k) {
+        //Count occurrence for each value
+        var dict = new Dictionary<int, int>();
+        for(int i=0; i<nums.Length; i++){
+            if(!dict.ContainsKey(nums[i])){
+                dict.Add(nums[i], 1);
+            }else {
+                dict[nums[i]]++;
+            }
+        }
+        
+        //Create array list indexed by occurrence
+        var numbersByCount = new List<int>[nums.Length+1];
+        foreach(var kv in dict){
+            var occurrence = kv.Value;
+            if(numbersByCount[occurrence] == null){
+               numbersByCount[occurrence] = new List<int>(); 
+            }
+            numbersByCount[occurrence].Add(kv.Key);
+        }
+        
+        //Decrease numbersByCount.Length as the number of occurence, and check the a sublist's existence
+        var res = new List<int>();
+        for(int i=numbersByCount.Length-1; i>0 && k>0; i--){
+            if(numbersByCount[i] != null){
+                res.AddRange(numbersByCount[i]);
+                k = k - numbersByCount[i].Count;
+            }
+        }
+        
+        return res.ToArray();
+    }
+}

README.md

@@ -22,8 +22,8 @@ Solutions in various programming languages are provided. Enjoy it.
 13. [Same Tree](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/13-Same-Tree): DFS
 14. [Angle Between Hands of a Clock](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/14-Angle-Between-Hands-of-a-Clock): Math
 15. [Reverse Words in a String](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/15-Reverse-Words-in-a-String): Pointer
-16. [16-Pow(x,n)](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/16-Pow(x,n)): Recursion
-
+16. [Pow(x,n)](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/16-Pow(x,n)): Recursion
+17. [Top K Frequent Elements](https://github.com/AlgoStudyGroup/Leetcode/tree/master/July-LeetCoding-Challenge/17-Top-K-Frequent-Elements): Bucket
 
 ## June LeetCoding Challenge
 Click [here](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge/) for problem descriptions.