# LeetCode Magical String

LeetCode Magical String

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

```class Solution {
public:
int magicalString(int n) {
string magic = "122";
int pos = 2;
while (magic.size() < n) {
switch (magic[magic.size()-1])
{
case '1':
magic += string(magic[pos] - '0', '2');
break;
case '2':
magic += string(magic[pos] - '0', '1');
break;
}
++pos;
}
int ans = 0;
for (int i = 0; i < n; ++i) {
ans += magic[i] == '1' ? 1 : 0;
}
return ans;
}
};
```