题解 | #字符串解码#

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 decodeString(string s) {
        // write code here
        int n = s.size();
        stack<char> st;
        for (int i = 0; i < n; ++i) {
            if (s[i] == ']') {
                string str = "", num = "";
                while (!st.empty() && st.top() != '[') {
                    str = st.top() + str;
                    st.pop();
                }
                st.pop();

                while (!st.empty() && isdigit(st.top())) {
                    num = st.top() + num;
                    st.pop();
                }
                int n = num == "" ? 1 : stoi(num);
                for (int j = 0; j < n; ++j) {
                    for (const auto &ch : str) {
                        st.emplace(ch);
                    }
                }
            } else {
                st.emplace(s[i]);
            }
        }

        string ans;
        while (!st.empty()) {
            ans = st.top() + ans;
            st.pop();
        }
        return ans;
    }
};