feat: add swift implementation to lcof problem: No.67 (#2962)

Author: klever34

lcof/面试题67. 把字符串转换成整数/README.md

@@ -282,6 +282,55 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func strToInt(_ str: String) -> Int {
+        let n = str.count
+        if n == 0 {
+            return 0
+        }
+
+        var index = str.startIndex
+        while index != str.endIndex && str[index] == " " {
+            index = str.index(after: index)
+        }
+
+        if index == str.endIndex {
+            return 0
+        }
+
+        var sign = 1
+        if str[index] == "-" {
+            sign = -1
+            index = str.index(after: index)
+        } else if str[index] == "+" {
+            index = str.index(after: index)
+        }
+
+        var result = 0
+        let flag = Int(Int32.max) / 10
+
+        while index != str.endIndex {
+            let char = str[index]
+            if char < "0" || char > "9" {
+                break
+            }
+
+            if result > flag || (result == flag && char > "7") {
+                return sign == 1 ? Int(Int32.max) : Int(Int32.min)
+            }
+
+            result = result * 10 + Int(char.asciiValue! - Character("0").asciiValue!)
+            index = str.index(after: index)
+        }
+
+        return sign * result
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题67. 把字符串转换成整数/Solution.swift

@@ -0,0 +1,44 @@
+class Solution {
+    func strToInt(_ str: String) -> Int {
+        let n = str.count
+        if n == 0 {
+            return 0
+        }
+
+        var index = str.startIndex
+        while index != str.endIndex && str[index] == " " {
+            index = str.index(after: index)
+        }
+
+        if index == str.endIndex {
+            return 0
+        }
+
+        var sign = 1
+        if str[index] == "-" {
+            sign = -1
+            index = str.index(after: index)
+        } else if str[index] == "+" {
+            index = str.index(after: index)
+        }
+
+        var result = 0
+        let flag = Int(Int32.max) / 10
+
+        while index != str.endIndex {
+            let char = str[index]
+            if char < "0" || char > "9" {
+                break
+            }
+
+            if result > flag || (result == flag && char > "7") {
+                return sign == 1 ? Int(Int32.max) : Int(Int32.min)
+            }
+
+            result = result * 10 + Int(char.asciiValue! - Character("0").asciiValue!)
+            index = str.index(after: index)
+        }
+
+        return sign * result
+    }
+}