Leetcode394. 字符串解码

class Solution {
public:
    string dfs(string s,int &idx)
    {
        string str;
        while(idx<s.size())
        {
            if(s[idx]==']')
            {
                idx++;
                return str;
            }
            else if(s[idx]>'0'&&s[idx]<='9')
            {
                string num;
                while(s[idx]>='0'&&s[idx]<='9')  num+=s[idx++];
                if(s[idx]=='[')
                {
                    int cnt=stoi(num);
                    string t=dfs(s,++idx);
                    while(cnt--)
                        str=str+t;
                }
            }
            else
                str+=s[idx++];
        } 
        return str;
    }
    string decodeString(string s) {
        int u=0;
        return dfs(s,u);
    }
};