<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) {
        stack<int> rep;
        stack<string> ch;
        s = "1[" + s + ']';
        for(int i = 0; i < s.length(); i++) {
            cout<<"s- "<<s[i]<<" ";
            if(isdigit(s[i])) {
                int num = 0;
                while(isdigit(s[i])) { 
                    num *= 10;
                    num += s[i] - '0';
                    i++;
                }
                cout<<"num "<<num<<endl;
                rep.push(num);
                string temp =  "";
                temp += s[i];
                ch.push(temp);
            } else {
                if(s[i] == ']') {
                    cout<<"solve - ";
                    string sub_st = "";
                    while(!ch.empty() && ch.top() != "[") {
                        sub_st = ch.top() + sub_st;
                        ch.pop();
                    }
                    cout<<sub_st<<endl;
                    int n = rep.top();
                    string new_st = "";
                    while(n--) {
                        new_st = sub_st + new_st;
                        // n--;
                    }
                    cout<<"solved - "<<new_st<<endl;
                    ch.pop();
                    rep.pop();
                    ch.push(new_st);
                } else {
                    string temp =  "";
                    temp += s[i];
                    ch.push(temp);
                    cout<<"char "<<ch.top()<<endl;
                }
            }
        }
        return ch.top();
    }
};
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