<p>Given a callable function <code>f(x, y)</code><strong>with a hidden formula</strong> and a value <code>z</code>, reverse engineer the formula and return <em>all positive integer pairs </em><code>x</code><em> and </em><code>y</code><em> where </em><code>f(x,y) == z</code>. You may return the pairs in any order.</p>
<p>While the exact formula is hidden, the function is monotonically increasing, i.e.:</p>
<ul>
<li><code>f(x, y) < f(x + 1, y)</code></li>
<li><code>f(x, y) < f(x, y + 1)</code></li>
</ul>
<p>The function interface is defined like this:</p>
<pre>
interface CustomFunction {
public:
// Returns some positive integer f(x, y) for two positive integers x and y based on a formula.
int f(int x, int y);
};
</pre>
<p>We will judge your solution as follows:</p>
<ul>
<li>The judge has a list of <code>9</code> hidden implementations of <code>CustomFunction</code>, along with a way to generate an <strong>answer key</strong> of all valid pairs for a specific <code>z</code>.</li>
<li>The judge will receive two inputs: a <code>function_id</code> (to determine which implementation to test your code with), and the target <code>z</code>.</li>
<li>The judge will call your <code>findSolution</code> and compare your results with the <strong>answer key</strong>.</li>
<li>If your results match the <strong>answer key</strong>, your solution will be <code>Accepted</code>.</li>
