添加 Swift 代码实现

animation-simulation/剑指offer/1的个数.md

@@ -200,6 +200,31 @@ class Solution {
 }
 ```
 
+Swift Code:
+
+```swift
+class Solution {
+    func countDigitOne(_ n: Int) -> Int {
+        var high = n, low = 0, cur = 0, count = 0, num = 1
+        while high != 0 || cur != 0 {
+            cur = high % 10
+            high /= 10
+            //这里我们可以提出 high * num 因为我们发现无论为几，都含有它 
+            if cur == 0 {
+                count += high * num
+            } else if cur == 1 { 
+                count += high * num + 1 + low
+            } else {
+                count += (high + 1) * num
+            }
+            low = cur * num + low
+            num *= 10
+        }
+        return count
+    }
+}
+```
+
 时间复杂度 : O(logn)  空间复杂度 O(1)