A magical string s consists of only '1' and '2' and obeys the following rules:
The first few elements of s is 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 is s itself.
Given an integer n, return the number of 1's in the first n number in the magical string s.
Examples
Example 1
Input: n = 6
Output: 3
Explanation: The first 6 elements of magical string s is "122112" and it contains three 1's, so return 3.
Example 2
Input: n = 1
Output: 1
Constraints
1 <= n <= 105
481. Magical String
Medium
30 Points
Two Pointers
String
A magical string s consists of only '1' and '2' and obeys the following rules:
The first few elements of s is 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 is s itself.
Given an integer n, return the number of 1's in the first n number in the magical string s.
Examples
Example 1
Input: n = 6
Output: 3
Explanation: The first 6 elements of magical string s is "122112" and it contains three 1's, so return 3.