_247.java

package com.fishercoder.solutions;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class _247 {
    public static class Solution1 {
        public List<String> findStrobogrammatic(int n) {
            return recursiveHelper(n, n);
        }

        private List<String> recursiveHelper(int n, int m) {
            if (n == 0) {
                return new ArrayList<>(Arrays.asList(""));
            }
            if (n == 1) {
                return new ArrayList<>(Arrays.asList("0", "1", "8"));
            }

            List<String> list = recursiveHelper(n - 2, m);
            List<String> res = new ArrayList<>();

            for (int i = 0; i < list.size(); i++) {
                String s = list.get(i);
                if (n != m) {
                    res.add("0" + s + "0");
                }
                res.add("1" + s + "1");
                res.add("6" + s + "9");
                res.add("8" + s + "8");
                res.add("9" + s + "6");
            }
            return res;
        }
    }
}