[C++知识库]字符串解码 3[a]2[bc]-算法题

题意：给定一个“编码”过的字符串，现将其解码；
解码规则：根据数字+字符串的形式将其完全展开即可
传送门

输入：s = “3[a]2[bc]”
输出：“aaabcbc”

题解：栈

string decodeString(string s) {
    vector<string> stk;
    int ptr = 0;
    while (ptr < s.size()) {
        char cur = s[ptr];
        if (isdigit(cur)) {
            string digits;
            while (isdigit(s[ptr]))
                digits += s[ptr++];
            stk.push_back(digits);
        } 
        else if (isalpha(cur) || cur == '[') {
            stk.push_back(string(1, s[ptr++])); 
        } 
        else {
            ++ptr;
            string res;
            while (1) {
                res = stk.back() + res;
                stk.pop_back();
                if (stk.back() == "[") {
                    stk.pop_back();
                    break;
                }
            }
            int repTime = stoi(stk.back()); 
            stk.pop_back();
            string tmp;
            while (repTime--) tmp += res;
            stk.push_back(tmp);
        }
    }
    string ret;
    for (auto &t : stk) ret += t;
    return ret;
}