1796. Second Largest Digit in a String

class Solution {
public:
    int secondHighest(string s) {
        string sn;
        for(int  i=0; i<s.size(); i++)
        {
            if(s[i]>=48 && s[i] <=57)
            {
               sn+=s[i];
            }
        }
        int max=0;
        for(int i=0; i<sn.size(); i++)
        {
           if(sn[i]-'0'>max)
           max=sn[i]-'0';
        }
        int max2=-1;
        for(int i=0; i<sn.size(); i++)
        {
            if(sn[i]-'0'>max2 && sn[i]-'0'<max)
            max2=sn[i]-'0';
        }

       return max2; 
    }
};