题解 | #牛牛的字符串解码问题#

#include <regex>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return string字符串
     */
    string decode_string(string& str, int& index) {
        if (str.empty()) return "";
        string substr;
        while(index < str.size())
        {
            string nums;
            if (str[index] >= '0' && str[index] <= '9') {
                nums += str[index];
                while (str[index + 1] >= '0' && str[index + 1] <= '9') {
                    ++index;
                    nums += str[index];
                }
                // point to 3, 递归
                index += 2;
                string strinter = decode_string(str, index);
                // 
                int num = 0;
                for (int j = 0; j < nums.size(); ++j) {
                    num += (int)(nums[j] - '0') * pow(10, j);
                }
                while (num != 0) {
                    substr.append(strinter);
                    --num;
                }


            }
            else if(str[index] == ']')
            {
                ++index;
                return substr;
            }
            else
            {
                substr += str[index];
                ++index;
            }
            
        }

        return substr;
    }

    string decodeString(string s) {
    int index = 0;
    return decode_string(s, index);
    }
};