[Swift]LeetCode409. 最長迴文串 | 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.

---

給定一個包含大寫字母和小寫字母的字符串，找到經過這些字母構形成的最長的迴文串。

在構造過程當中，請注意區分大小寫。好比 "Aa" 不能當作一個迴文字符串。

注意:
假設字符串的長度不會超過 1010。

示例 1:

輸入:
"abccccdd"

輸出:
7

解釋:
咱們能夠構造的最長的迴文串是"dccaccd", 它的長度是 7。

---

20ms

 1 class Solution {
 2     func longestPalindrome(_ s: String) -> Int {
 3         //
 4         var arr:[Int] = Array(repeating: 0,count: 128)
 5         //遍歷字符串
 6         for char in s.characters
 7         {
 8             arr[char.toInt()] += 1
 9         }
10         var ans:Int = 0
11         //遍歷數組
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擴展代碼  
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 }