add leetcode problem-cn part1

算法题（国内版）/problem (English)/n 的第 k 个因子(English) [the-kth-factor-of-n].html

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+<p>You are given two positive integers <code>n</code> and <code>k</code>. A factor of an integer <code>n</code> is defined as an integer <code>i</code> where <code>n % i == 0</code>.</p>
+
+<p>Consider a list of all factors of <code>n</code> sorted in <strong>ascending order</strong>, return <em>the </em><code>k<sup>th</sup></code><em> factor</em> in this list or return <code>-1</code> if <code>n</code> has less than <code>k</code> factors.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 12, k = 3
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> Factors list is [1, 2, 3, 4, 6, 12], the 3<sup>rd</sup> factor is 3.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 7, k = 2
+<strong>Output:</strong> 7
+<strong>Explanation:</strong> Factors list is [1, 7], the 2<sup>nd</sup> factor is 7.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 4, k = 4
+<strong>Output:</strong> -1
+<strong>Explanation:</strong> Factors list is [1, 2, 4], there is only 3 factors. We should return -1.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= k &lt;= n &lt;= 1000</code></li>
+</ul>