feat: add swift implementation to lcof2 problem: No.087 (#3472)

Author: klever34

lcof2/剑指 Offer II 087. 复原 IP/README.md

@@ -288,6 +288,45 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    private var n: Int = 0
+    private var s: String = ""
+    private var ans: [String] = []
+    private var t: [String] = []
+
+    func restoreIpAddresses(_ s: String) -> [String] {
+        n = s.count
+        self.s = s
+        dfs(0)
+        return ans
+    }
+
+    private func dfs(_ i: Int) {
+        if i >= n && t.count == 4 {
+            ans.append(t.joined(separator: "."))
+            return
+        }
+        if i >= n || t.count >= 4 {
+            return
+        }
+        var x = 0
+        let chars = Array(s)
+        for j in i..<min(i + 3, n) {
+            x = x * 10 + Int(chars[j].wholeNumberValue!)
+            if x > 255 || (chars[i] == "0" && i != j) {
+                break
+            }
+            t.append(String(chars[i...j]))
+            dfs(j + 1)
+            t.removeLast()
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 087. 复原 IP/Solution.swift

@@ -0,0 +1,34 @@
+class Solution {
+    private var n: Int = 0
+    private var s: String = ""
+    private var ans: [String] = []
+    private var t: [String] = []
+
+    func restoreIpAddresses(_ s: String) -> [String] {
+        n = s.count
+        self.s = s
+        dfs(0)
+        return ans
+    }
+
+    private func dfs(_ i: Int) {
+        if i >= n && t.count == 4 {
+            ans.append(t.joined(separator: "."))
+            return
+        }
+        if i >= n || t.count >= 4 {
+            return
+        }
+        var x = 0
+        let chars = Array(s)
+        for j in i..<min(i + 3, n) {
+            x = x * 10 + Int(chars[j].wholeNumberValue!)
+            if x > 255 || (chars[i] == "0" && i != j) {
+                break
+            }
+            t.append(String(chars[i...j]))
+            dfs(j + 1)
+            t.removeLast()
+        }
+    }
+}