## Algorithm

Problem Name: 481. 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 `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`

## Code Examples

### #1 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const magicalString = function(n) {
const queue = []
let one = true
let count1 = 0
while (n-- > 0) {
queue.shift()
let c = one ? 1 : 2
one = !one
queue.push(c)
count1 += 2 - c
if (queue[0] === 2 && n-- > 0) {
queue.push(c)
count1 += 2 - c
}
}
return count1
}
``````
Copy The Code &

Input

cmd
n = 6

Output

cmd
3

### #2 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution(object):
def magicalString(self, n):
cnt, s, two = 0, "1", True
for i in range(n - 1):
if s[i] == "1":
cnt += 1
s += "2" if two else "1"
else: s += "22" if two else "11"
two = not two
return cnt if n != 1 else 1
``````
Copy The Code &

Input

cmd
n = 6

Output

cmd
3