 # [LeetCode] 248. Strobogrammatic Number III

## 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<Character, Character> map = new HashMap<>();
map.put('0', '0');
map.put('1', '1');
map.put('6', '9');
map.put('8', '8');
map.put('9', '6');
List<String> 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<Character, Character> map, String low, String high, char[] buffer, int left, int right, List<String> 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++;
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);
}
}
}
``````