LeetCode 1088. Confusing Number II

Problem Statement

Backtrack.

impl Solution {
    fn rotate(xx: i64) ->i64 {
        let (mut x, mut y) = (xx, 0);
        while x != 0 {
            let mut k = x % 10;
            if k == 6 {
                k = 9;
            } else if k == 9 {
                k = 6;
            }
            y = y * 10 + k;
            x = x / 10;
        }
        return y;
    }

    fn search(num: i64, n: i32, ans: &mut i32) {
        if num > n as i64 {
            return;
        }
        if num != 0 {
            if num != Self::rotate(num) {
                *ans += 1;
            }
            Self::search(num * 10, n, ans);
        }
        Self::search(num * 10 + 1, n, ans);
        Self::search(num * 10 + 6, n, ans);
        Self::search(num * 10 + 8, n, ans);
        Self::search(num * 10 + 9, n, ans);
    }
    pub fn confusing_number_ii(n: i32) -> i32 {
        let mut ans = 0;
        Self::search(0, n, &mut ans);
        return ans;
    }
}