Update0077.组合，添加C#

problems/0077.组合.md

@@ -792,7 +792,59 @@ def backtracking(result, path, n, j, k)
 end
 
 ```
-
+### C#
+```C#
+// 暴力
+public class Solution
+{
+    public IList<IList<int>> res = new List<IList<int>>();
+    public IList<int> path = new List<int>();
+    public IList<IList<int>> Combine(int n, int k)
+    {
+        BackTracking(n, k, 1);
+        return res;
+    }
+    public void BackTracking(int n, int k, int start)
+    {
+        if (path.Count == k)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = start; i <= n; i++)
+        {
+            path.Add(i);
+            BackTracking(n, k, i + 1);
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+// 剪枝
+public class Solution
+{
+    public IList<IList<int>> res = new List<IList<int>>();
+    public IList<int> path = new List<int>();
+    public IList<IList<int>> Combine(int n, int k)
+    {
+        BackTracking(n, k, 1);
+        return res;
+    }
+    public void BackTracking(int n, int k, int start)
+    {
+        if (path.Count == k)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = start; i <= n - (k - path.Count) + 1; i++)
+        {
+            path.Add(i);
+            BackTracking(n, k, i + 1);
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+```
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