Pipes实现LeetCode(193.验证电话号码)

[LeetCode] 193.Valid Phone Numbers 验证电话号码

Given a text file file.txt that contains list of phone numbers (one per line), write a one liner bash script to print all valid phone numbers.

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)

You may also assume each line in the text file must not contain leading or trailing white spaces.

For example, assume that file.txt has the following content:

987-123-4567
123 456 7890
(123) 456-7890

Your script should output the following valid phone numbers:

987-123-4567
(123) 456-7890

这道题让我们验证数字串是否为正确的电话号码的格式,而且规定了正确的格式只有两种(xxx) xxx-xxxx or xxx-xxx-xxxx,那么我们可以看出来区别就是在前几个字符,而后八个字符都相同。这题有多种解法,我们首先来看使用awk命令的解法。这道题是难点是如何写匹配的正则表达式。那么首先来看‘/.../'表示中间的是要匹配的正则表达式,然后脱字符^匹配一行的开头,美元符$在正则表达式中匹配行尾,然后再看中间的部分,[0-9]{3}表示匹配三个数字,圆括号括起一组正则表达式. 它和"|"操作符或在用expr进行子字符串提取(substring extraction)一起使用很有用。那么([0-9]{3}-|\([0-9]{3}\) )就可以理解了,它匹配了xxx-和(xxx) 这两种形式的字符串,然后后面的就好理解了,匹配xxx-xxxx这样的字符串,参见代码如下:

解法一:

awk '/^([0-9]{3}-|\([0-9]{3}\) )[0-9]{3}-[0-9]{4}$/' file.txt

下面来看使用sed命令的解法。那么我们先来看后面的两个参数,-n表示关闭默认输出,默认将自动打印所有行,这样就不会打印出不符合要求的数字串了。-r表示支持扩展正则+ ? () {} |。后面的正则表达式和上面都相同,就是后面多了一个p,在用sed时,p和-n合用,表示打印某一行,这样才能把符合要求的行打印出来:

解法二:

sed -n -r '/^([0-9]{3}-|\([0-9]{3}\) )[0-9]{3}-[0-9]{4}$/p' file.txt

再来看使用grep命令的做法。我没有查到那个-P参数的用法,有没有大神来点拨一下,后面的正则表达式思路根上面的相同,只不过用d{3}来表示[0-9]{3},道理都一样,参见代码如下:

解法三:

grep -P '^(\d{3}-|\(\d{3}\) )\d{3}-\d{4}$' file.txt

参考资料:

https://leetcode.com/discuss/29282/this-is-my-simple-solution

https://leetcode.com/discuss/29476/three-different-solutions-using-grep-sed-and-awk

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