[Swift]LeetCode38.报数|CountandSay

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The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     111221

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

报数序列是指一个整照其中的整数的顺序进数序列，按行报数，得到下一个数。其前五项如下：

1.     1
2.     11
3.     21
4.     1211
5.     111221

1 被读作 "one 1" ("一个一") , 即 11。
11 被读作 "two 1s" ("两个一"）, 即 21。
21 被读作 "one 2", "one 1" （"一个二" , "一个一") , 即 1211。

给定一个正整数 n（1 ≤ n ≤ 30），输出报数序列的第 n 项。

注意：整数顺序将表示为一个字符串。

示例 1:

输入: 1
输出: "1"

示例 2:

输入: 4
输出: "1211"

12ms

1 class Solution {
2     func countAndSay(_ n: Int) -> String {
3         let 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4         return ans[n]
5     }
6 }

16ms

 1 class Solution {
 2     func countAndSay(_ n: Int) -> String {
 3         var num = "1"
 4         if n == 1 {
 5             return "1"
 6         }
 7         for _ in 1..<n {
 8             var newStr = String()
 9             let arrayOfStr = Array(num)
10             var count = 1
11             for i in 0..<arrayOfStr.count {
12                 if i == arrayOfStr.count - 1 {
13                     newStr += "\(count)\(arrayOfStr[i])"
14                 } else {
15                     if arrayOfStr[i] == arrayOfStr[i + 1] {
16                         count += 1
17                     } else {
18                         newStr += "\(count)\(arrayOfStr[i])"
19                         count = 1
20                     }
21                 }
22             }
23             num = newStr
24         }
25         return num
26     }
27 }

16ms

 1 class Solution {
 2     func countAndSay(_ n: Int) -> String {
 3         if (n == 1 || n > 30){
 4             return "1"
 5         }
 6         var resultString:String = ""
 7         let ReadStr = countAndSay(n-1)
 8         var characterArray = [Character](ReadStr)
 9         var repeatTime = 1
10         for i in 0..<characterArray.count {
11             if i == 0 {
12                 if characterArray.count == 1 {
13                     resultString.append(String(repeatTime) + String(characterArray[i]))
14                     repeatTime = 1
15                 }
16                 continue
17             }
18             if characterArray[i] == characterArray[i - 1] {
19                 repeatTime = repeatTime + 1
20             } else {
21                 resultString.append(String(repeatTime) + String(characterArray[i - 1]))
22                 repeatTime = 1
23             }
24             
25             if i == characterArray.count - 1 {
26                 resultString.append(String(repeatTime) + String(characterArray[i]))
27             }
28         }
29         return resultString
30     }
31 }

20ms

 1 class Solution {
 2     func countAndSay(_ n: Int) -> String {
 3           guard n > 0 else{
 4             return ""
 5         }
 6         
 7         var result = "1"
 8         for _ in 1..<n{
 9             let resultCharArray = [Character](result)
10             var count = 1
11             var current = ""
12             for i in 1..<resultCharArray.count{
13                 if resultCharArray[i] == resultCharArray[i - 1]{
14                     count += 1
15                 }else{
16                     current.append("\(count)")
17                     current.append(resultCharArray[i - 1])
18                     count = 1
19                 }
20             }
21             current.append(count == 0 ? "" : "\(count)")
22             current.append(resultCharArray.last!)
23             result = current
24         }
25         return result
26     }
27 }

24ms

 1 class Solution {
 2     func countAndSay(input: String) -> String {
 3         var lastChar: Character?
 4         var count = 0
 5         var result: String = ""
 6         
 7         input.forEach { (char) in
 8             if let myLastChar = lastChar {
 9                 if char != myLastChar {
10                     result = result + String(count) + String(myLastChar)
11                     lastChar = char
12                     count = 1
13                 } else {
14                     count += 1
15                 }
16             } else {
17                 lastChar = char
18                 count = 1
19             }
20         }
21         
22         if let lastChar = lastChar {
23             result = result + String(count) + String(lastChar)
24         }
25         
26         return result
27     }
28     
29     func countAndSay(_ n: Int) -> String {
30         var result = "1"
31         (1..<n).forEach { (_) in
32             result = countAndSay(input: result)
33         }
34         
35         return result
36     }
37 }

24ms

 1 class Solution {
 2     func countAndSay(_ n: Int) -> String {
 3         var resultArray:[Int] = [1]
 4         var tempArray:[Int] = []
 5         var result = ""
 6         for i in 0..<(n - 1) {
 7             var count = 0   //重复数字的计数
 8             var number = -1
 9             var index = 0
10             let length = resultArray.count
11             while index < length {
12                 number = resultArray[index]
13                 for j in index..<length {
14                     if resultArray[j] == number {
15                         count += 1
16                         continue
17                     }
18                     break
19                 }
20                 tempArray.append(count)
21                 tempArray.append(number)
22                 index = index + count
23                 count = 0
24             }
25             resultArray = tempArray
26             tempArray.removeAll()
27         }
28         for i in resultArray {
29             result = result + "\(i)"
30         }
31         return result
32     }
33 }

40ms

 1 /*
 2  理解题意：
 3  n=1时输出字符串1；
 4  n=2时，数上次字符串中的数值个数，因为上次字符串有1个1，所以输出11；
 5  n=3时，由于上次字符是11，有2个1，所以输出21；
 6  n=4时，由于上次字符串是21，有1个2和1个1，所以输出1211。
 7  依次类推
 8  */
 9 
10 import Foundation
11 
12 class Solution {
13     func say(_ say: String) -> String {
14         
15         var chars = Array(say)
16         var count = 1
17         var tmpSay = ""
18         
19         for i in 0..<chars.count {
20             if i < chars.count - 1 && chars[i] == chars[i+1]{
21                 count = count + 1
22             }else{
23                 tmpSay.append("\(count)")
24                 tmpSay.append("\(chars[i])")
25                 count = 1
26             }
27         }
28         return tmpSay
29     }
30     func countAndSay(_ n: Int) -> String {
31         if n == 1 {
32             return "1"
33         }
34         var sayStr = countAndSay(1)
35         
36         for _ in 1..<n {
37             sayStr = say(sayStr)
38         }
39         
40         return sayStr
41     }
42 }