(n: i32, k: i32)
| 6 | |
| 7 | impl Solution { |
| 8 | pub fn get_permutation(n: i32, k: i32) -> String { |
| 9 | let (mut n, mut k) = (n as usize, k as usize - 1); |
| 10 | let mut x: Vec<char> = (b'1'..).take(n).map(char::from).collect(); |
| 11 | let mut buf = vec![]; |
| 12 | loop { |
| 13 | let zone = Self::factorial(n - 1); |
| 14 | let choice = k / zone; |
| 15 | buf.push(x.remove(choice)); |
| 16 | k -= choice * zone; |
| 17 | n -= 1; |
| 18 | if n == 0 { break buf } |
| 19 | } .iter().collect() |
| 20 | } |
| 21 | |
| 22 | /// used for small num a: a! |
| 23 | pub fn factorial(n: usize) -> usize { |