# Solution based on Strobogrammatic Number II

• Strobogrammatic Number II give us all the strings with length n, then we can call it to get strings with length between low.length() and high.length(), and remove the strings that less than low and larger than high.

public class Solution {
public int strobogrammaticInRange(String low, String high) {
int m = low.length(), n = high.length();
List<String> result = new ArrayList<String>();
for(int i=m; i<=n; i++){
}
int i=0;
int count=result.size();
while(i<result.size() && result.get(i).length()==low.length()){
if(result.get(i).compareTo(low)<0){
count--;
}
i++;
}
i=result.size()-1;
while(i>=0 && result.get(i).length()==high.length()){
if(result.get(i).compareTo(high)>0){
count--;
}
i--;
}
return count;
}
public List<String> findStrobogrammatic(int n) {
HashMap<Character, Character> map = new HashMap<>();
map.put('1','1');
map.put('0','0');
map.put('6','9');
map.put('9','6');
map.put('8','8');
List<String> list = new ArrayList<>();
char[] arr = new char[n];
dfs(list, arr, 0, n, map);
Collections.sort(list);
return list;
}
public void dfs(List<String> list, char[] buffer, int idx, int n, Map<Character, Character> map){
if(idx==(n+1)/2){
return;
}
for(char key:map.keySet()){
if(idx==0 && n>1 && key=='0'){
continue;
}
if(idx==(n/2) && (key=='6'||key=='9')){
continue;
}
buffer[idx] = key;
buffer[n-idx-1] = map.get(key);
dfs(list, buffer, idx+1, n, map);
}
}

}

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