<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 multiplyStr(string s,int num){
        string str = "";
        while(num){
            str = str + s;
            num--;
        }
        return str;
    }
    void makeNumberAndPush(string s, int *idx,stack <int> &numStk){
        string num = "";
        while(s[(*idx)] >= '0' && s[(*idx)] <= '9'){
            num = num + s[(*idx)];
            (*idx)++;
        }
        (*idx)--;
        numStk.push(stoi(num));
    }
    void takeOut(stack <string> &chStk,stack<int> &numStk){
        string s = "";
        while(chStk.top() != "["){
            s = chStk.top() + s;
            chStk.pop();
        }
        chStk.pop();
        s = multiplyStr(s,numStk.top());
        numStk.pop();
        chStk.push(s);
    }
    string makeStr(stack <string> &chStk){
        string s = "";
        while(!chStk.empty()){
            s = chStk.top() + s;
            chStk.pop();
        }
        return s;
    }
    string decodeString(string s) {
        stack <int> numStk;
        stack <string> chStk;
        string result = "";
        int n = s.size();
        for(int i = 0; i < n ;i++){
            if(s[i] >= '0' && s[i] <= '9'){
                makeNumberAndPush(s,&i,numStk);
            }
            else if(s[i] != ']'){
                
                string ch(1,s[i]);
                chStk.push(ch);
            }
            else if(s[i] == ']'){
                takeOut(chStk,numStk);
            }
            
        }
        result = makeStr(chStk);
        return result;
    }
};
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