README.md

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 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.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn magical_string(n: i32) -> i32 {
        let mut magical = vec![];
        let mut elem = true;
        let mut ret = 0;

        for i in 0..(n as usize) {
            magical.push(elem);
            match magical[i] {
                true => ret += 1,
                false => magical.push(elem),
            }
            elem = !elem;
        }

        ret
    }
}