<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 {
public:
    string addStrings(string num1, string num2) {
        reverse(num1.begin() , num1.end());
        reverse(num2.begin() , num2.end());
        string ans = "";
        int i = 0; 
        int j = 0;
        int carry = 0;
        while(i<num1.size() && j< num2.size())
        {
            int ith = num1[i] - '0';
            int jth = num2[j] - '0';

            int temp = ith + jth + carry;
            carry = 0;
            if(temp > 9 )
            {
                carry = 1;
            }
            ans += to_string(temp%10);
            i++;
            j++;
        }

        while(i<num1.size())
        {
            int ith = num1[i] - '0' + carry;
            carry = 0;
            if(ith > 9)
            {
                carry = 1;
            }
            
            ans += to_string(ith%10);
            i++;
        }

        while(j<num2.size())
        {
            int jth = num2[j] - '0' + carry ;
            carry = 0;
            if(jth > 9)
            {
                carry = 1;
            }
            
            ans += to_string(jth%10);
            j++;
        }
        if(carry)
        {
            ans += to_string(carry);
        }

        reverse(ans.begin() , ans.end());
        return ans;
    }
};
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