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.
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| public class Solution {
private char[] validNumbers = new char[]{'0', '1', '6', '8', '9'};
private char[] singleable = new char[]{'0', '1', '8'};
public int strobogrammaticInRange(String low, String high) {
assert low != null && high != null;
int ll = low.length();
int hl = high.length();
int result = 0;
if(ll > hl || (ll == hl&&low.compareTo(high) > 0)) {
return 0;
}
List<String> list = findStrobogrammatic(ll);
if (ll == hl) {
for (String s : list) {
if (s.compareTo(low) >= 0 && s.compareTo(high) <= 0) {
result++;
}
if (s.compareTo(high) > 0) {
break;
}
}
} else {
for (int i = list.size() - 1; i >= 0; i--) {
String s = list.get(i);
if (s.compareTo(low) >= 0) {
result++;
}
if (s.compareTo(low) < 0) {
break;
}
}
list = findStrobogrammatic(hl);
for (String s : list) {
if (s.compareTo(high) <= 0) {
result++;
}
if (s.compareTo(high) > 0) {
break;
}
}
for (int i = ll + 1; i < hl; i++) {
result += findStrobogrammatic(i).size();
}
}
return result;
}
public List<String> findStrobogrammatic(int n) {
assert n > 0;
List<String> result = new ArrayList<>();
if (n == 1) {
for (char c : singleable) {
result.add(String.valueOf(c));
}
return result;
}
if (n % 2 == 0) {
helper(n, new StringBuilder(), result);
} else {
helper(n - 1, new StringBuilder(), result);
List<String> tmp = new ArrayList<>();
for (String s : result) {
for (char c : singleable) {
tmp.add(new StringBuilder(s).insert(s.length() / 2, c).toString());
}
}
result = tmp;
}
return result;
}
private void helper(int n, StringBuilder sb, List<String> result) {
if (sb.length() > n) return;
if (sb.length() == n) {
if (sb.length() > 0 && sb.charAt(0) != '0') {
result.add(sb.toString());
}
return;
}
for (char c : validNumbers) {
StringBuilder tmp = new StringBuilder(sb);
String s = "" + c + findMatch(c);
tmp.insert(tmp.length() / 2, s);
helper(n, tmp, result);
}
}
private char findMatch(char c) {
switch (c) {
case '1':
return '1';
case '6':
return '9';
case '9':
return '6';
case '8':
return '8';
case '0':
return '0';
default:
return 0;
}
}
}
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