<p>Given two non-negative integers, <code>num1</code> and <code>num2</code> represented as string, return <em>the sum of</em> <code>num1</code> <em>and</em> <code>num2</code> <em>as a string</em>.</p>

<p>You must solve the problem without using any built-in library for handling large integers (such as <code>BigInteger</code>). You must also not convert the inputs to integers directly.</p>

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

<pre>
<strong>Input:</strong> num1 = &quot;11&quot;, num2 = &quot;123&quot;
<strong>Output:</strong> &quot;134&quot;
</pre>

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

<pre>
<strong>Input:</strong> num1 = &quot;456&quot;, num2 = &quot;77&quot;
<strong>Output:</strong> &quot;533&quot;
</pre>

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

<pre>
<strong>Input:</strong> num1 = &quot;0&quot;, num2 = &quot;0&quot;
<strong>Output:</strong> &quot;0&quot;
</pre>

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

<ul>
	<li><code>1 &lt;= num1.length, num2.length &lt;= 10<sup>4</sup></code></li>
	<li><code>num1</code> and <code>num2</code> consist of only digits.</li>
	<li><code>num1</code> and <code>num2</code> don&#39;t have any leading zeros except for the zero itself.</li>
</ul>

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        dif = abs(len(num2) - len(num1))
        if len(num1) < len(num2):
            add = dif*'0' + num1
            num1 = add
        else:
            add = dif*'0' + num2
            num2 = add

        n = max(len(num1), len(num2))
        resp = ''
        sobe = 0
        for i in range(n-1, -1, -1):
            parcial_sum = sobe + (int(num1[i]) + int(num2[i]))
            fica = parcial_sum % 10
            sobe = parcial_sum // 10
            resp += str(fica)

        if sobe > 0:
            resp = resp + str(sobe)

        ans = ''
        for i in range(len(resp)-1, -1, -1):
            ans += resp[i]
            
        return ans
        
16300