国外版

算法题（国外版）/rotated-digits.html

@@ -0,0 +1,43 @@
+<p>An integer <code>x</code> is a <strong>good</strong> if after rotating each digit individually by 180 degrees, we get a valid number that is different from <code>x</code>. Each digit must be rotated - we cannot choose to leave it alone.</p>
+
+<p>A number is valid if each digit remains a digit after rotation. For example:</p>
+
+<ul>
+	<li><code>0</code>, <code>1</code>, and <code>8</code> rotate to themselves,</li>
+	<li><code>2</code> and <code>5</code> rotate to each other (in this case they are rotated in a different direction, in other words, <code>2</code> or <code>5</code> gets mirrored),</li>
+	<li><code>6</code> and <code>9</code> rotate to each other, and</li>
+	<li>the rest of the numbers do not rotate to any other number and become invalid.</li>
+</ul>
+
+<p>Given an integer <code>n</code>, return <em>the number of <strong>good</strong> integers in the range </em><code>[1, n]</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 10
+<strong>Output:</strong> 4
+<strong>Explanation:</strong> There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
+Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 1
+<strong>Output:</strong> 0
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 2
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
+</ul>