[Swift]LeetCode744. 尋找比目標字母大的最小字母 | Find Smallest Letter Greater Than Target

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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Given a list of sorted characters letterscontaining only lowercase letters, and given a target letter target, find the smallest element in the list that is larger than the given target.

Letters also wrap around. For example, if the target is target = 'z' and letters = ['a', 'b'], the answer is 'a'.

Examples:

Input:
letters = ["c", "f", "j"]
target = "a"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "c"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "d"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "g"
Output: "j"

Input:
letters = ["c", "f", "j"]
target = "j"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "k"
Output: "c"

Note:

1. letters has a length in range [2, 10000].
2. letters consists of lowercase letters, and contains at least 2 unique letters.
3. target is a lowercase letter.

---

給定一個只包含小寫字母的有序數組letters 和一個目標字母 target，尋找有序數組裏面比目標字母大的最小字母。

數組裏字母的順序是循環的。舉個例子，若是目標字母target = 'z' 而且有序數組爲 letters = ['a', 'b']，則答案返回 'a'。

示例:

輸入:
letters = ["c", "f", "j"]
target = "a"
輸出: "c"

輸入:
letters = ["c", "f", "j"]
target = "c"
輸出: "f"

輸入:
letters = ["c", "f", "j"]
target = "d"
輸出: "f"

輸入:
letters = ["c", "f", "j"]
target = "g"
輸出: "j"

輸入:
letters = ["c", "f", "j"]
target = "j"
輸出: "c"

輸入:
letters = ["c", "f", "j"]
target = "k"
輸出: "c"

注:

1. letters長度範圍在[2, 10000]區間內。
2. letters 僅由小寫字母組成，最少包含兩個不一樣的字母。
3. 目標字母target 是一個小寫字母。

---

Runtime: 220 ms

Memory Usage: 19.8 MB

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3         if target >= letters.last!
 4         {
 5             return letters[0]
 6         }
 7         var n:Int = letters.count
 8         var left:Int = 0
 9         var right:Int = n
10         while (left < right)
11         {
12             var mid:Int = left + (right - left) / 2
13             if letters[mid] <= target
14             {
15                 left = mid + 1
16             }
17             else
18             {
19                 right = mid
20             }
21         }
22         return letters[right]
23     }
24 }

---

252ms

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3     var left = 0
 4     var right = letters.count
 5     while left < right {
 6         let temp = (left + right) / 2
 7         if letters[temp] > target{
 8             right = temp
 9         }else{
10             left = temp + 1
11         }
12     }
13     
14     return letters[left % letters.count]
15     }
16 }

---

272ms

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3 
 4             if letters.isEmpty {
 5             return target
 6         }
 7         
 8         guard let codeTarget = target.unicodeScalars.first?.value else {
 9             return target
10         }
11         
12         guard let codeLettersLast = letters[letters.count - 1].unicodeScalars.first?.value else {
13             return target
14         }
15         
16         if codeLettersLast <= codeTarget {
17             
18             return letters[0]
19             
20         } else {
21             
22             for letter in letters {
23                 guard let code = letter.unicodeScalars.first?.value else {
24                     continue
25                 }
26                 
27                 if code > codeTarget {
28                     return letter
29                 }
30             }
31             
32         }
33         
34         return target
35     }
36 }

---

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3         for letter in letters{
 4             if (letter > target){
 5                 return letter
 6             }
 7         }
 8         return letters[0]
 9     }
10     
11 }

---

284ms

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3         let zValue = "z".unicodeScalars.first!.value
 4         var targetValue = target.unicodeScalars.first!.value
 5         var minV:UInt32 = zValue + 1
 6         var minC:Character?
 7         for letter in letters{
 8             let letterValue = letter.unicodeScalars.first!.value
 9             if letterValue > targetValue,
10             letterValue < minV{
11                 minV = letterValue
12                 minC = letter
13             }
14         }
15         return minC ?? letters[0]
16     }
17 }

---

288ms

 1 class Solution {
 2     func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
 3         var answer:Character = letters[0]
 4         
 5         for (index,letter) in letters.enumerated(){
 6             if letter <= target{
 7                 if index < letters.count - 1{
 8                 answer = letters[index + 1]}
 9                 if index == letters.count - 1{
10                     answer = letters[0]
11                 }}
12         }
13         
14         return answer
15     }
16 }