README.md

1238. Circular Permutation in Binary Representation

Given 2 integers n and start. Your task is return any permutation p of (0,1,2.....,2^n -1) such that :

• p[0] = start
• p[i] and p[i+1] differ by only one bit in their binary representation.
• p[0] and p[2^n -1] must also differ by only one bit in their binary representation.

Example 1:

Input: n = 2, start = 3
Output: [3,2,0,1]
Explanation: The binary representation of the permutation is (11,10,00,01). 
All the adjacent element differ by one bit. Another valid permutation is [3,1,0,2]

Example 2:

Input: n = 3, start = 2
Output: [2,6,7,5,4,0,1,3]
Explanation: The binary representation of the permutation is (010,110,111,101,100,000,001,011).

Constraints:

• 1 <= n <= 16
• 0 <= start < 2 ^ n

Solutions (Rust)

1. Solution

impl Solution {
    pub fn circular_permutation(n: i32, start: i32) -> Vec<i32> {
        let mut x = 1;
        let mut start_index = 0;
        let mut ret = vec![0];

        for _ in 0..n {
            let rev = ret.iter().rev().map(|&num| num + x).collect::<Vec<i32>>();
            for i in 0..rev.len() {
                ret.push(rev[i]);
                if rev[i] == start {
                    start_index = ret.len() - 1;
                }
            }
            x *= 2;
        }

        ret.rotate_left(start_index);

        ret
    }
}