<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 {
// find si and ei to solve
    pair<int,int> getIndexesToSolve(string s) {
        pair<int,int> indexes;
        int bracketStart = 0;
        for(int i=0;i<s.length();i++) {
            if(s[i]== '[') {
                bracketStart = i;
            }
            if(s[i]==']') {
                indexes.second=i;
                break;
            }
        }
        while(bracketStart>0 && isdigit(s[bracketStart-1])) {
            bracketStart--;
        }
        indexes.first=bracketStart;
        return indexes;
    }    

// get conversted string
    string convertString(string s) {
        int num = s[0] - '0';
        bool numDone = false;
        string sub;
        for(int i=1;i<s.length()-1;i++) {
            if(s[i] == '[') {
                numDone = true;
                continue;
            }
            if(!numDone) {
                num = (num * 10) + (s[i] - '0');
            } else {
                sub=sub + s[i];
            }
        }
        string result;
        while(num>0) {
            result = result + sub;
            num--;
        }
        return result;
    }

// replace string
    string replace(string original,pair<int,int> indexes, string decoded) {
        string result;
        for(int i=0;i<original.length();i++) {
            if (i==indexes.first) {
                result = result + decoded;
                i=indexes.second + 1;
            }
            result = result + original[i];
        }
        return result;
    }

public:
    string decodeString(string s) {
        string result = s;
        while(result.contains('[')) {
            pair<int,int> indexes = getIndexesToSolve(result);
            string toBeDecoded = result.substr(indexes.first,(indexes.second-indexes.first + 1));
            string decoded = convertString(toBeDecoded);
            result = replace(result,indexes,decoded);
        }

        return result.c_str();
        
    }
};
10500