[Swift]LeetCode481. 神奇字符串 | Magical String_app

概述A magical string S consists of only ‘1‘ and ‘2‘ and obeys the following rules: The string S is magical because concatenating the number of contiguous occurrences of characters ‘1‘ and ‘2‘ generates th

A magical string S consists of only ‘1‘ and ‘2‘ and obeys the following rules:

The string S is magical because concatenating the number of contiguous occurrences of characters ‘1‘ and ‘2‘ generates the string Sitself.

The first few elements of string S is the following: S = "1221121221221121122……"

If we group the consecutive ‘1‘s and ‘2‘s in S,it will be:

1 22 11 2 1 22 1 22 11 2 11 22 ......

and the occurrences of ‘1‘s or ‘2‘s in each group are:

1 2 2 1 1 2 1 2 2 1 2 2 ......

You can see that the occurrence sequence above is the S itself.

Given an integer N as input,return the number of ‘1‘s in the first N number in the magical string S.

Note: N will not exceed 100,000.

Example 1:

input: 6Output: 3Explanation: The first 6 elements of magical string S is "12211" and it contains three 1‘s,so return 3.

神奇的字符串 S 只包含 ‘1‘ 和 ‘2‘，并遵守以下规则：

字符串 S 是神奇的，因为串联字符 ‘1‘ 和 ‘2‘ 的连续出现次数会生成字符串 S 本身。

字符串 S 的前几个元素如下：S = “1221121221221121122 ......”

如果我们将 S 中连续的 1 和 2 进行分组，它将变成：

1 22 11 2 1 22 1 22 11 2 11 22 ......

并且每个组中 ‘1‘ 或 ‘2‘ 的出现次数分别是：

1 2 2 1 1 2 1 2 2 1 2 2 ......

你可以看到上面的出现次数就是 S 本身。

给定一个整数 N 作为输入，返回神奇字符串 S 中前 N 个数字中的 ‘1‘ 的数目。

注意：N 不会超过 100,000。

示例：

输入：6输出：3解释：神奇字符串 S 的前 6 个元素是 “12211”，它包含三个 1，因此返回 3。

Runtime: 20 ms Memory Usage: 10.1 MB

 1 class Solution { 2     func magicalString(_ n: Int) -> Int { 3         if n <= 0 {return 0} 4         if n <= 3 {return 1} 5         var res:Int = 1 6         var head:Int = 2 7         var tail:Int = 3 8         var num:Int = 1 9         var v:[Int] = [1,2,2]10         while(tail < n)11         {12             for i in 0..<v[head]13             {14                 v.append(num)15                 if num == 1 && tail < n16                 {17                     res += 118                 }19                 tail += 120             }21             num ^= 322             head += 123         }24         return res25     }26 }

124ms

 1 class Solution { 2     func magicalString(_ n: Int) -> Int { 3     var sequence = [Int]() 4     sequence.append(contentsOf: [1,2]) 5     var groups = 2 6     var result = 1 7     if(n==0){return 0} 8     while sequence.count<n { 9         if(sequence[groups]==1){10             result += sequence.last! == 1 ? 0:111             sequence.append(sequence.last! == 1 ? 2:1)12             groups+=113         }else{14             let temp = sequence.last! == 1 ? 2:115             sequence.append(contentsOf: [temp,temp])16             result += temp == 1 ? 2:017             groups+=118         }19     }20     if(sequence.count==n){return result}else{21         result -= sequence.last! == 1 ? 1:022         return result23     }24   }25 }