One edit distance
 bool isOneEditDistance(string &s, string &t) {
        // write your code here
        int n= t.length(), m= s.size();
        if(m>n)
            return isOneEditDistance(t,s);
        if(n-m >1)
            return false;
        int i=0;
        int shift= n-m;
        while(i<m &&s[i]==t[i])
            i++;
        if(i==m)
            return shift>0;
        if(shift==0)
            i++;
        while(i<m && s[i]==t[i+shift])
            i++;
        return i==m;
    }
};