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.
For example,
Given low = "50", high = "100", return 3. Because 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.
1 public class Solution {
2 private int count = 0;
3 public int strobogrammaticInRange(String low, String high) {
4 find(low, high, "");
5 find(low, high, "0");
6 find(low, high, "1");
7 find(low, high, "8");
8 return count;
9 }
10 private void find(String low, String high, String s){
11 //all possible strobogrammatic numbers that are needed to account for
12 //must have the length of [low.length(), high.length()]
13 if(s.length() >= low.length() && s.length() <= high.length()){
14 //ignore the numbers that have the same length with low but are
15 //smaller than low. Similarly, ignore the numbers that have the
16 //same length with high but are bigger than high
17 if(s.length() == low.length() && s.compareTo(low) < 0 ||
18 s.length() == high.length() && s.compareTo(high) > 0){
19 return;
20 }
21 //ignore the cases where s.equals("0") == false && s.charAt(0) == '0'
22 if(!(s.length() > 1 && s.charAt(0) == '0')){
23 count++;
24 }
25 }
26 //recursion exit condition: if s.length() is already bigger than the
27 //upper bound length, then there is no need to keep searching, exit!
28 else if(s.length() > high.length()){
29 return;
30 }
31 find(low, high, "0" + s + "0");
32 find(low, high, "1" + s + "1");
33 find(low, high, "6" + s + "9");
34 find(low, high, "8" + s + "8");
35 find(low, high, "9" + s + "6");
36 }
37 }
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