Add C# solutions

README.md

@@ -16,6 +16,9 @@ Solutions in various programming languages are provided. Enjoy it.
 7. [Word Pattern](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/07-Word-Pattern)
 8. [Sum of Root To Leaf Binary Numbers](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/08-Sum-of-Root-To-Leaf-Binary-Numbers)
 9. [Compare Version Numbers](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/09-Compare-Version-Numbers)
+10. [Bulls and Cows](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/10-Bulls-and-Cows)
+11. [Maximum Product Subarray](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/11-Maximum-Product-Subarray)
+12. [Combination Sum III](https://github.com/AlgoStudyGroup/Leetcode/tree/master/September-LeetCoding-Challenge/12-Combination-Sum-III)
 
 ## August LeetCoding Challenge
 Click [here](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge/) for problem descriptions.

September-LeetCoding-Challenge/10-Bulls-and-Cows/Bulls-and-Cows.cs

@@ -0,0 +1,20 @@
+public class Solution {
+    public string GetHint(string secret, string guess) {
+        var bulls = 0;
+        var cows = 0;
+        int[] secretarr = new int[10];
+		int[] guessarr = new int[10];
+        for(int i=0; i<secret.Length; i++){
+            if(secret[i] == guess[i]){
+                bulls++;
+            }else {
+                ++secretarr[secret[i] - '0'];
+				++guessarr[guess[i] - '0'];
+            }
+        }
+        for (int i = 0; i < 10; ++i) {
+			cows += Math.Min(secretarr[i], guessarr[i]);
+		}
+        return bulls + "A" + cows + "B";
+    }
+}

September-LeetCoding-Challenge/11-Maximum-Product-Subarray/Maximum-Product-Subarray.cs

@@ -0,0 +1,17 @@
+public class Solution {
+    public int MaxProduct(int[] nums)
+    {
+        int s = nums[0];
+        int r = nums[0];
+
+        for(int i=1, max = s, min = s; i<nums.Length; i++){
+            int temp = max;
+            max = Math.Max(Math.Max(nums[i] * max, nums[i] * min), nums[i]);
+            min = Math.Min(Math.Min(nums[i] * temp, nums[i] * min), nums[i]);
+
+            r = Math.Max(max, r);
+        }
+
+        return r;
+    }
+}

September-LeetCoding-Challenge/12-Combination-Sum-III/Combination-Sum-III.cs

@@ -0,0 +1,26 @@
+public class Solution {
+        public IList<IList<int>> CombinationSum3(int k, int n)
+        {
+            var res = new List<IList<int>>();
+            var tmp = new List<int>();
+            Backtrack(res, tmp, k, n, 1);
+            return res;
+        }
+
+        public void Backtrack(List<IList<int>> res, List<int> tmp, int k, int n, int idx)
+        {
+            if (k == tmp.Count && n == 0)
+            {
+                res.Add(new List<int>(tmp)); //Deep clone
+                return;
+            }
+
+            for (int i = idx; i <= n && k > 0 && n > 0; i++)
+            {
+                if(i>9) break;
+                tmp.Add(i);
+                Backtrack(res, tmp, k, n - i, i + 1);
+                tmp.RemoveAt(tmp.Count - 1); //Remove last item when it doesn't find the correct combo
+            }
+        }
+}