問題描述

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].

自己寫的程式：

#include<iostream>
#include<string>
#include<unordered_map>
using namespace std;
class
 
 Solution {
public:
    string decodeString(string s) {
        string s2;
        int k1=0;
        int k2=0;
        int k3=0;
        int i=0;
        int num;
        while (i < s.size())
        {
            num = 0;
            int j = i;
            while (s[j]!='['&&j<s.size())
            {
                num = num * 10
 
 + s[j] - '0';
                j++;
            }
            k2 = j+1;
            while(s[j]!=']'&&j<s.size())
            {
                j++;
            }
            k3 = j-1;

            while(num>0)
            {
                for (int i = k2;i <=k3;i++)
                    s2.push_back(s[i]);
                num--;
            }

            i = j+1;
        }
        return s2;
    }
};
void main()
{
    Solution s;
    string a = "3[a]2[b]";
    cout << s.decodeString(a) << endl;

}

注：只針對沒有巢狀的字串序列，在寫程式的時候j=i++，和j=i+1有很大的不一樣。

參考的程式
class Solution {
public:
string decodeString(string s, int& i) {
string res;

    while (i < s.length() && s[i] != ']') {
        if (!isdigit(s[i]))
            res += s[i++];
        else {
            int n = 0;
            while (i < s.length() && isdigit(s[i]))
                n = n * 10 + s[i++] - '0';

            i++; // '['
            string t = decodeString(s, i);
            i++; // ']'

            while (n-- > 0)
                res += t;
        }
    }

    return res;
}

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

};