# 0415. Add Strings

<https://leetcode.com/problems/add-strings>

## Description

Given two non-negative integers, `num1` and `num2` represented as string, return *the sum of* `num1` *and* `num2` *as a string*.

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

**Example 1:**

```
**Input:** num1 = "11", num2 = "123"
**Output:** "134"
```

**Example 2:**

```
**Input:** num1 = "456", num2 = "77"
**Output:** "533"
```

**Example 3:**

```
**Input:** num1 = "0", num2 = "0"
**Output:** "0"
```

**Constraints:**

* `1 <= num1.length, num2.length <= 104`
* `num1` and `num2` consist of only digits.
* `num1` and `num2` don't have any leading zeros except for the zero itself.

## ac

```java
```


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