[Swift]LeetCode744. 寻找比目标字母大的最小字母 | Find Smallest Letter Greater Than Target

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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.

---

给定一个只包含小写字母的有序数组letters 和一个目标字母 target，寻找有序数组里面比目标字母大的最小字母。

数组里字母的顺序是循环的。举个例子，如果目标字母target = 'z' 并且有序数组为 letters = ['a', 'b']，则答案返回 'a'。

示例:

输入:
letters = ["c", "f", "j"]
target = "a"
输出: "c"

输入:
letters = ["c", "f", "j"]
target = "c"
输出: "f"

输入:
letters = ["c", "f", "j"]
target = "d"
输出: "f"

输入:
letters = ["c", "f", "j"]
target = "g"
输出: "j"

输入:
letters = ["c", "f", "j"]
target = "j"
输出: "c"

输入:
letters = ["c", "f", "j"]
target = "k"
输出: "c"

注:

1. letters长度范围在[2, 10000]区间内。
2. letters 仅由小写字母组成，最少包含两个不同的字母。
3. 目标字母target 是一个小写字母。

---

Runtime: 220 ms

Memory Usage: 19.8 MB

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
        if target >= letters.last!
        {
            return letters[0]
        }
        var n:Int = letters.count
        var left:Int = 0
        var right:Int = n
        while (left < right)
        {
            var mid:Int = left + (right - left) / 2
            if letters[mid] <= target
            {
                left = mid + 1
            }
            else
            {
                right = mid
            }
        }
        return letters[right]
    }
}

---

252ms

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
    var left = 0
    var right = letters.count
    while left < right {
        let temp = (left + right) / 2
        if letters[temp] > target{
            right = temp
        }else{
            left = temp + 1
        }
    }
    
    return letters[left % letters.count]
    }
}

---

272ms

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {

            if letters.isEmpty {
            return target
        }
        
        guard let codeTarget = target.unicodeScalars.first?.value else {
            return target
        }
        
        guard let codeLettersLast = letters[letters.count - 1].unicodeScalars.first?.value else {
            return target
        }
        
        if codeLettersLast <= codeTarget {
            
            return letters[0]
            
        } else {
            
            for letter in letters {
                guard let code = letter.unicodeScalars.first?.value else {
                    continue
                }
                
                if code > codeTarget {
                    return letter
                }
            }
            
        }
        
        return target
    }
}

---

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
        for letter in letters{
            if (letter > target){
                return letter
            }
        }
        return letters[0]
    }
    
}

---

284ms

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
        let zValue = "z".unicodeScalars.first!.value
        var targetValue = target.unicodeScalars.first!.value
        var minV:UInt32 = zValue + 1
        var minC:Character?
        for letter in letters{
            let letterValue = letter.unicodeScalars.first!.value
            if letterValue > targetValue,
            letterValue < minV{
                minV = letterValue
                minC = letter
            }
        }
        return minC ?? letters[0]
    }
}

---

288ms

class Solution {
    func nextGreatestLetter(_ letters: [Character], _ target: Character) -> Character {
        var answer:Character = letters[0]
        
        for (index,letter) in letters.enumerated(){
            if letter <= target{
                if index < letters.count - 1{
                answer = letters[index + 1]}
                if index == letters.count - 1{
                    answer = letters[0]
                }}
        }
        
        return answer
    }
}