Watch 10 video solutions for Magical String, a medium level problem involving Two Pointers, String. This walkthrough by Greg Hogg has 443,129 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
A magical string s consists of only '1' and '2' and obeys the following rules:
'1' and '2' generates the string s itself.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.
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