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leetcode/problem/happy-number.html

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+<p>Write an algorithm to determine if a number <code>n</code> is happy.</p>
+
+<p>A <strong>happy number</strong> is a number defined by the following process:</p>
+
+<ul>
+	<li>Starting with any positive integer, replace the number by the sum of the squares of its digits.</li>
+	<li>Repeat the process until the number equals 1 (where it will stay), or it <strong>loops endlessly in a cycle</strong> which does not include 1.</li>
+	<li>Those numbers for which this process <strong>ends in 1</strong> are happy.</li>
+</ul>
+
+<p>Return <code>true</code> <em>if</em> <code>n</code> <em>is a happy number, and</em> <code>false</code> <em>if not</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 19
+<strong>Output:</strong> true
+<strong>Explanation:</strong>
+1<sup>2</sup> + 9<sup>2</sup> = 82
+8<sup>2</sup> + 2<sup>2</sup> = 68
+6<sup>2</sup> + 8<sup>2</sup> = 100
+1<sup>2</sup> + 0<sup>2</sup> + 0<sup>2</sup> = 1
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 2
+<strong>Output:</strong> false
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= n &lt;= 2<sup>31</sup> - 1</code></li>
+</ul>