670\. Maximum Swap

Medium

You are given an integer `num`. You can swap two digits at most once to get the maximum valued number.

Return _the maximum valued number you can get_.

**Example 1:**

**Input:** num = 2736

**Output:** 7236

**Explanation:** Swap the number 2 and the number 7.

**Example 2:**

**Input:** num = 9973

**Output:** 9973

**Explanation:** No swap.

**Constraints:**

*   <code>0 <= num <= 10<sup>8</sup></code>