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输入:a = "11", b = "1"
输出："100"

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输入：a = "1010", b = "1011"
输出："10101"

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struct Solution;

// @lc code=start
use std::iter;

impl Solution {
    /// ## 解题思路
    /// - iterator
    pub fn add_binary(a: String, b: String) -> String {
        // 处理长度
        let (a, b) = match (a.len(), b.len()) {
            (la, lb) if la > lb => (a, b),
            _ => (b, a),
        };

        let a = format!("0{}", a);

        //
        let ab = a
            .chars()
            .rev()
            .zip(b.chars().rev().chain(iter::repeat('0')))
            .scan(0_u32, |carry, (x, y)| {
                let s = x as u32 + y as u32 + *carry % 2;
                *carry = s / 2;
                Some(char::from_digit(s % 2, 2))
            })
            .map(|c| c.unwrap_or('0'))
            .collect::<String>()
            .chars()
            .rev()
            .collect::<String>();

        if ab.len() > 1 && ab.starts_with('0') {
            String::from(&ab[1..])
        } else {
            ab
        }
    }
}
// @lc code=end

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test() {
        assert_eq!(
            Solution::add_binary("11".into(), "1".into()),
            "100".to_string()
        );
    }
}