<p>You are given an integer <code>num</code>. You can swap two digits at most once to get the maximum valued number.</p>

<p>Return <em>the maximum valued number you can get</em>.</p>

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

<pre>
<strong>Input:</strong> num = 2736
<strong>Output:</strong> 7236
<strong>Explanation:</strong> Swap the number 2 and the number 7.
</pre>

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

<pre>
<strong>Input:</strong> num = 9973
<strong>Output:</strong> 9973
<strong>Explanation:</strong> No swap.
</pre>

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

<ul>
	<li><code>0 &lt;= num &lt;= 10<sup>8</sup></code></li>
</ul>

class Solution {
public:
    int maximumSwap(int num) {
        string numStr = to_string(num);

        vector<int> last(10,-1);

        for (int i = 0; i < numStr.size(); ++i) {
            last[numStr[i] - '0'] = i;
        }

        for (int i = 0; i < numStr.size(); ++i) {
            for (int d = 9; d > numStr[i] - '0'; --d) {
                if (last[d] > i) {
                    swap(numStr[i], numStr[last[d]]);
                    return stoi(numStr);
                }
            }
        }

        return num;
    }
};
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