Method permute

46. Permutations/src/main.rs:8–15

(nums: Vec<i32>)

impl Solution {
    pub fn permute(nums: Vec<i32>) -> Vec<Vec<i32>> {
        let mut res = vec![vec![]];
        for &i in nums.iter() {
            Self::permute_add(&mut res, i);
        }
        res.sort();
        res
    }

    pub fn permute_add(permutation: &mut Vec<Vec<i32>>, elem: i32) {
        if permutation.len() == 0 {