<p>Given an encoded string, return its decoded string.</p>

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

<p>You may assume that the input string is always valid; there are 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, <code>k</code>. For example, there will not be input like <code>3a</code> or <code>2[4]</code>.</p>

<p>The test cases are generated so that the length of the output will never exceed <code>10<sup>5</sup></code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;3[a]2[bc]&quot;
<strong>Output:</strong> &quot;aaabcbc&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;3[a2[c]]&quot;
<strong>Output:</strong> &quot;accaccacc&quot;
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;2[abc]3[cd]ef&quot;
<strong>Output:</strong> &quot;abcabccdcdcdef&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 30</code></li>
	<li><code>s</code> consists of lowercase English letters, digits, and square brackets <code>&#39;[]&#39;</code>.</li>
	<li><code>s</code> is guaranteed to be <strong>a valid</strong> input.</li>
	<li>All the integers in <code>s</code> are in the range <code>[1, 300]</code>.</li>
</ul>

class Solution {
public:
    string decodeString(string s) {
        cout << s << endl;

        if(s.empty()){
            return "";
        } 

        if(s[0] >= 'a' && s[0] <= 'z'){
            string sub;
            int i = 0;
            while(s[i] >= 'a' && s[i] <= 'z'){
                sub.push_back(s[i]);
                i++;
            }

            return sub + decodeString(s.substr(i));
        }

        int count = stoi(s);
        int n = 1 + log10(count) + 1;
        int start = n;
        int open = 1;
        while(open != 0){
            if(s[n] == '['){
                open++;
            } 
            if(s[n] == ']'){
                open--;
            } 
            n++;
        }
        string sub = s.substr(start, n - start - 1);
        string res = decodeString(sub);
        string ans;
        for(int i = 0; i < count; i++){
            ans += res;
        }

        ans += decodeString(s.substr(n));

        return ans;
    }
};
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