Update0093.复原IP地址，添加C#

problems/0093.复原IP地址.md

@@ -799,6 +799,53 @@ object Solution {
   }
 }
 ```
+### C#
+```csharp
+public class Solution
+{
+    public IList<string> res = new List<string>();
+    public IList<string> RestoreIpAddresses(string s)
+    {
+        if (s.Length < 4 || s.Length > 12) return res;
+        BackTracking(s, 0, 0);
+        return res;
+    }
+    public void BackTracking(string s, int start, int pointSum)
+    {
+        if (pointSum == 3)
+        {
+            if (IsValid(s, start, s.Length - 1))
+            {
+                res.Add(s);
+            }
+            return;
+        }
+        for (int i = start; i < s.Length; i++)
+        {
+            if (IsValid(s, start, i))
+            {
+                s = s.Insert(i + 1, ".");
+                BackTracking(s, i + 2, pointSum + 1);
+                s = s.Remove(i + 1, 1);
+            }
+            else break;
+        }
+    }
+    public bool IsValid(string s, int start, int end)
+    {
+        if (start > end) return false;
+        if (s[start] == '0' && start != end) return false;
+        int num = 0;
+        for (int i = start; i <= end; i++)
+        {
+            if (s[i] > '9' || s[i] < '0') return false;
+            num = num * 10 + s[i] - '0';
+            if (num > 255) return false;
+        }
+        return true;
+    }
+}
+```
 
 
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