Problem

A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Write a function to count the total strobogrammatic numbers that exist in the range of low <= num <= high.

Example:

Input: low = "50", high = "100"

Output: 3 Explanation: 69, 88, and 96 are three strobogrammatic numbers.Note:Because the range might be a large number, the low and high numbers are represented as string.

Solution

class Solution {    int count = 0;    public int strobogrammaticInRange(String low, String high) {        Map
    
      map = new HashMap<>();        map.put('0', '0');        map.put('1', '1');        map.put('6', '9');        map.put('8', '8');        map.put('9', '6');        List
     
       res = new ArrayList<>();        for (int len = low.length(); len <= high.length(); len++) {            dfs(map, low, high, new char[len], 0, len-1, res);        }        System.out.println(res);        return count;            }        private void dfs(Map
      
        map, String low, String high, char[] buffer, int left, int right, List
       
         res) {        if (left > right) {            String num = new String(buffer);            if ((num.length() == low.length() && num.compareTo(low) < 0) ||               (num.length() == high.length() && num.compareTo(high) > 0)) {                return;            }            count++;            res.add(num);            return;        }                for (char ch: map.keySet()) {            if (buffer.length != 1 && left == 0 && ch == '0') continue;            if (left == right && ch != map.get(ch)) continue;            buffer[left] = ch;            buffer[right] = map.get(ch);            dfs(map, low, high, buffer, left+1, right-1, res);        }    }}