Update 0860.柠檬水找零，添加C#

Author: 涛 陈

problems/0860.柠檬水找零.md

@@ -397,6 +397,46 @@ object Solution {
   }
 }
 ```
+### C#
+```csharp
+public class Solution
+{
+    public bool LemonadeChange(int[] bills)
+    {
+        int five = 0, ten = 0, twenty = 0;
+        foreach (var bill in bills)
+        {
+            if (bill == 5) five++;
+            if (bill == 10)
+            {
+                if (five == 0) return false;
+                five--;
+                ten++;
+            }
+            if (bill == 20)
+            {
+                if (ten > 0 && five > 0)
+                {
+                    ten--;
+                    five--;
+                    twenty++;
+                } 
+                else if (five >= 3)
+                {
+                    five -= 3;
+                    twenty++;
+                }
+                else
+                {
+                    return false;
+                }
+
+            }
+        }
+        return true;
+    }
+}
+```
 
 
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