[Swift]LeetCode409. 最长回文串 | Longest Palindrome

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Given a string which consists of lowercase or uppercase letters, find the length of the longest palindromes that can be built with those letters.

This is case sensitive, for example "Aa" is not considered a palindrome here.

Note:
Assume the length of given string will not exceed 1,010.

Example:

Input:
"abccccdd"

Output:
7

Explanation:
One longest palindrome that can be built is "dccaccd", whose length is 7.

---

给定一个包含大写字母和小写字母的字符串，找到经过这些字母构形成的最长的回文串。

在构造过程当中，请注意区分大小写。好比 "Aa" 不能当作一个回文字符串。

注意:
假设字符串的长度不会超过 1010。

示例 1:

输入:
"abccccdd"

输出:
7

解释:
咱们能够构造的最长的回文串是"dccaccd", 它的长度是 7。

---

20ms

 1 class Solution {
 2     func longestPalindrome(_ s: String) -> Int {
 3         //
 4         var arr:[Int] = Array(repeating: 0,count: 128)
 5         //遍历字符串
 6         for char in s.characters
 7         {
 8             arr[char.toInt()] += 1
 9         }
10         var ans:Int = 0
11         //遍历数组
12         for i in 0..<128
13         {
14             ans += arr[i] / 2 * 2
15             if ans % 2 == 0 && arr[i] % 2 == 1
16             {
17                 ans += 1
18             }
19         }
20         return ans
21     }
22 }
23     //Character扩展代码  
24     extension Character  
25     {  
26         func toInt() -> Int  
27         {  
28             var num:Int = Int()
29             for scalar in String(self).unicodeScalars  
30             {  
31                 num = Int(scalar.value)  
32             }  
33             return num  
34         }  
35     }

---

28ms

 1 class Solution {
 2     func longestPalindrome(_ s: String) -> Int {
 3         var map: [Bool] = Array(repeating: false, count: 128)
 4         var length = 0
 5         for char in s.unicodeScalars {
 6             let value = Int(char.value)
 7             map[value] = !map[value]
 8             if !map[value] {
 9                 length += 2
10             }
11         }
12 
13         if length < s.count {
14             length += 1
15         }
16 
17         return length
18     }
19 }

---

28ms

 1 class Solution {
 2     struct CharTracker {
 3             let c: Character
 4             let n: Int
 5         }
 6     func longestPalindrome(_ s: String) -> Int {
 7         var charTracker: [CharTracker] = [CharTracker]()
 8         var pSum = 0
 9         var firstSwitch: Bool = true
10         var cSet = [Character : Int]()
11         s.forEach {
12             cSet[$0, default: 0] += 1
13         }
14         for (_, n) in cSet {
15             if (n & 1) == 0 {
16                 pSum += n
17             } else {
18                 pSum += n - 1
19                 if (firstSwitch) {
20                     pSum += 1
21                     firstSwitch = false
22                 }
23             }
24         }
25         return pSum
26     }
27 }

---

32ms

 1 class Solution {
 2     func longestPalindrome(_ s: String) -> Int {
 3         var frequencyTable = [Character:Int]()
 4         for ch in s {
 5             frequencyTable[ch] = (frequencyTable[ch] ?? 0) + 1
 6         }
 7         
 8         var count = 0
 9         for (key,value) in frequencyTable {
10             if value%2 == 1 {
11                 count += (value-1)
12                 frequencyTable[key] = 1
13             } else {
14                 count += value
15                 frequencyTable[key] = 0
16             }
17         }
18         
19         for (_,value) in frequencyTable {
20             if value%2 == 1 {
21                 count += 1
22                 break
23             }
24         }
25         
26         return count
27     }
28 }

---

36ms

 1 class Solution {
 2     func longestPalindrome(_ s: String) -> Int {
 3         var longestPalindrome = 0
 4         var singleChar = 0
 5     
 6         // check that the string is not empty
 7         guard s.count > 0 else { return 0 }
 8         
 9         // if there is only 1 character, return 1
10         if s.count == 1 {
11             return 1
12         }
13     
14         // there can be 1 odd character included
15         // the rest can only be included in multiples of 2
16         // create a hashmap to keep track of the number of occurances
17         var characters = [Character: Int]()
18         for char in s {
19             if let count = characters[char] {
20                 characters[char] = count + 1
21             } else {
22                 characters[char] = 1
23             }
24         }
25     
26         // if there's a 1 or modulo > 0, set a variable to 1
27         // loop through the characters and divide by 2
28         for key in characters.keys {
29             if characters[key]! % 2 != 0 {
30                 singleChar = 1
31             }
32         
33             longestPalindrome += characters[key]! / 2 * 2
34             // divide by 2 to eliminate remainders
35         }
36     
37         longestPalindrome += singleChar
38     
39         return longestPalindrome
40     }
41 }