添加0509斐波那契数C#版本

problems/0509.斐波那契数.md

@@ -370,5 +370,45 @@ object Solution {
 }
 ```
 
+### C#
+
+动态规划:
+
+```c#
+public class Solution
+{
+    public int Fib(int n)
+    {
+        if(n<2) return n;
+        int[] dp = new int[2] { 0, 1 };
+        for (int i = 2; i <= n; i++)
+        {
+            int temp = dp[0] + dp[1];
+            dp[0] = dp[1];
+            dp[1] = temp;
+        }
+        return dp[1];
+    }
+}
+```
+
+递归:
+
+```c#	
+public class Solution
+{
+    public int Fib(int n)
+    {
+        if(n<2)
+            return n;
+        return Fib(n-1)+Fib(n-2);
+    }
+}
+```
+
+
+
+
+
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