[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:

letters has a length in range [2, 10000].
letters consists of lowercase letters, and contains at least 2 unique letters.
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:

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

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 }