[Swift]LeetCode93. 复原IP地址 | Restore IP Addresses

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

Example:

Input: "25525511135"
Output: ["255.255.11.135", "255.255.111.35"]

示例:

输入: "25525511135"
输出: ["255.255.11.135", "255.255.111.35"]

16ms

 1 class Solution {
 2     func restoreIpAddresses(_ s: String) -> [String] {
 3         if s.characters.count < 4 || s.characters.count > 12 {
 4             return []
 5         }
 6
 7         let characters = Array(s.characters)
 8         var result = [String]()
 9         var candidate = [String]()
10
11         backtracking(characters, 0, &candidate, &result)
12
13         return result
14     }
15     private func backtracking(_ characters: [Character], _ pos: Int, _ candidate: inout [String], _ result: inout [String]) {
16         if candidate.count == 4 {
17             result.append(candidate.joined(separator: "."))
18             return
19         }
20
21         let charsLeft = characters.count - pos
22         let groupsLeft = 4 - candidate.count
23         let minLen = groupsLeft == 1 ? charsLeft - groupsLeft + 1 : 1
24         let maxLen = characters[pos] == "0" ? 1 : min(3, charsLeft - groupsLeft + 1)
25
26         if minLen > maxLen {
27             return
28         }
29
30         for len in minLen...maxLen {
31             let num = String(characters[pos..<(pos + len)])
32             if Int(num)! > 255 {
33                 continue
34             }
35             candidate.append(num)
36             backtracking(characters, pos + len, &candidate, &result)
37             candidate.removeLast()
38         }
39     }
40 }

原文地址：https://www.cnblogs.com/strengthen/p/9936814.html