394_Decode_String

Decode String

Difficulty Medium

tags recur

Given an encoded string, return it's decoded string.

The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer.

You may assume that the input string is always valid; No extra white spaces, square brackets are well-formed, etc.

Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k. For example, there won't be input like 3a or 2[4].

Examples:

s = "3[a]2[bc]", return "aaabcbc".
s = "3[a2[c]]", return "accaccacc".
s = "2[abc]3[cd]ef", return "abcabccdcdcdef".

递归问题

solution 1

class Solution {
public:
    string decodeString(string s) {
        string res;
        int p = 0, n = s.size();
        while (p < n) {
            if (s[p] - '0' < 0 || s[p] - '0' > 9) {
                // original code mode
                res.push_back(s[p++]);
            } else {
                // repeat mode
                int p_r = p;
                while (s[p] - '0' >= 0 && s[p] - '0' <= 9) {
                    p++;
                }
                int r_cnt = stoi(s.substr(p_r, p-p_r));
                int p_br = ++p; 
                int br_stk = 1;
                while (br_stk > 0) {
                    if (s[p] == ']') {
                        br_stk--;
                    } 
                    if (s[p] == '[') {
                        br_stk++;
                    }
                    p++;
                }
                string r_string = s.substr(p_br, p-1-p_br);
                for (int i=0; i<r_cnt; i++) {
                    res = res + decodeString(r_string);
                }
            }
            
        }
        return res;
    }
};