add leetcode problem-cn part6

算法题（国内版）/problem (English)/有效电话号码(English) [valid-phone-numbers].html

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+<p>Given a text file <code>file.txt</code> that contains a list of phone numbers (one per line), write a one-liner bash script to print all valid phone numbers.</p>
+
+<p>You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)</p>
+
+<p>You may also assume each line in the text file must not contain leading or trailing white spaces.</p>
+
+<p><strong>Example:</strong></p>
+
+<p>Assume that <code>file.txt</code> has the following content:</p>
+
+<pre>
+987-123-4567
+123 456 7890
+(123) 456-7890
+</pre>
+
+<p>Your script should output the following valid phone numbers:</p>
+
+<pre>
+987-123-4567
+(123) 456-7890
+</pre>