problem

We have two special characters:

  • The first character can be represented by one bit 0.
  • The second character can be represented by two bits (10 or 11).

Given a binary array bits that ends with 0, return true if the last character must be a one-bit character.

 

Example 1:

Input: bits = [1,0,0]
Output: true
Explanation: The only way to decode it is two-bit character and one-bit character.
So the last character is one-bit character.

Example 2:

Input: bits = [1,1,1,0]
Output: false
Explanation: The only way to decode it is two-bit character and two-bit character.
So the last character is not one-bit character.

 

Constraints:

  • 1 <= bits.length <= 1000
  • bits[i] is either 0 or 1.

submission

impl Solution {
    pub fn is_one_bit_character(bits: Vec<i32>) -> bool {
        // solution count 1s from the right end
        bits.into_iter()
            .rev()
            .skip(1)
            .take_while(|&b| b == 1)
            .count() % 2 == 0
        // my original solution with state machine
        // enum State {
        //     None,
        //     Current2Bit,
        //     Last1Bit,
        //     Last2Bit,
        // }
        // matches!(
        //     bits.into_iter()
        //         .fold(State::None, |s, v| match (s, v) {
        //             (State::Current2Bit, _) => State::Last2Bit,
        //             (_, 0) => State::Last1Bit,
        //             _ => State::Current2Bit,
        //         }),
        //     State::Last1Bit
        // )
    }
}