Update 0459.重复的子字符串，添加C#版

problems/0459.重复的子字符串.md

@@ -681,6 +681,32 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 前缀表不减一
+public bool RepeatedSubstringPattern(string s)
+{
+    if (s.Length == 0)
+        return false;
+    int[] next = GetNext(s);
+    int len = s.Length;
+    if (next[len - 1] != 0 && len % (len - next[len - 1]) == 0) return true;
+    return false;
+}
+public int[] GetNext(string s)
+{
+    int[] next = Enumerable.Repeat(0, s.Length).ToArray();
+    for (int i = 1, j = 0; i < s.Length; i++)
+    {
+        while (j > 0 && s[i] != s[j])
+            j = next[j - 1];
+        if (s[i] == s[j])
+            j++;
+        next[i] = j;
+    }
+    return next;
+}
+```
 
 
 <p align="center">