248. Strobogrammatic Number III ---------H

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.

A:
就是找到所有长度为从1 到 high.length() 的string， 然后比较就可以了。 

（这里， C++ string，是可以直接比较的）

class Solution {
public:
    int strobogrammaticInRange(string low, string high) {
        while(low.length()<high.length()){
            low = "0"+low;
        }
        while(high.length()<low.length()){ // in case high < low
            high = "0"+high;
        }
        int count = 0;
        for(int i =1;i<=high.length();i++){
            for(auto str : getAll(i,i)){
                while(str.length() < high.length()){ // first make same length
                    str = "0"+str;
                }
                if(str >= low  && str <= high)
                    count++;
            }
        }        
        return count;
    }
private:
    vector<string> getAll(int n, const int N){// current n, total N
        if(n==0)
            return vector<string>{""};
        if(n==1){
            return vector<string>{"0","1","8"};
        }
        vector<string> res;
        for(auto ss : getAll(n-2, N)){
            if(n != N){
                res.push_back("0"+ss+"0");
            }
            res.push_back("1"+ss+"1");
            res.push_back("8"+ss+"8");
            res.push_back("6"+ss+"9");
            res.push_back("9"+ss+"6");
        }
        return res;
    }    
};

Mistakes：

这里，比较蛋疼的，就是 给的参数， high < low 。 这个得都变成string,再判断