LeetCode: Valid Palindrome 题解

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

 

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

主要考察， cctype.h 的使用：

可能用到的函数： tolower, toupper, isalpha, isdigit, isalnum。

 1 class Solution {

 2 public:

 3     bool isPalindrome(string s) {

 4         int left=0,right =s.size()-1;

 5         while(left<right)

 6         {

 7             if(!isalnum(s[left]))    

 8                 left++;

 9             else if(!isalnum(s[right]))

10                 right--;

11             else

12             {

13                 if(tolower(s[left])==tolower(s[right]))

14                 {

15                     left++;

16                     right--;

17                 }

18                 else

19                     return false;

20             }

21         }

22         return true;        

23     }

24 };

可能用到的函数： tolower, toupper, isalpha, isdigit, isalnum。

补充知识:  cctype 库文件(参考cplusplus: http://www.cplusplus.com/reference/cctype/ )

函数名	function description	函数说明
isalnum	Check if character is alphanumeric (function )	查看参数是否为字符或数字
isalpha	Check if character is alphabetic (function )	查看参数是否为字符
isblank	Check if character is blank (function )	查看参数是否为空格
iscntrl	Check if character is a control character (function )	查看参数是否为控制字符
isdigit	Check if character is decimal digit (function )	查看参数是否为十进制数字
isgraph	Check if character has graphical representation (function )	查看参数是否为可显示字符
islower	Check if character is lowercase letter (function )	查看参数是否为可打印字符
isprint	Check if character is printable (function )	查看参数是否为小写字符
ispunct	Check if character is a punctuation character (function )	查看参数是否为标点符号
isspace	Check if character is a white-space (function )	查看参数是否为空字符
isupper	Check if character is uppercase letter (function )	查看参数是否为大写字符
isxdigit	Check if character is hexadecimal digit (function )	查看参数是否为十六进制数字

具体的ASCII 与 cctype各函数的对应关系如下表： 

ASCII values

characters

iscntrl

isblank

isspace

isupper

islower

isalpha

isdigit

isxdigit

isalnum

ispunct

isgraph

isprint

x00 .. 0x08

NUL, (other control codes)

x

0x09

tab ('\t')

x

x

x

0x0A .. 0x0D

(white-space control codes:'\f','\v','\n','\r')

x

x

0x0E .. 0x1F

(other control codes)

x

0x20

space (' ')

x

x

x

0x21 .. 0x2F

!"#$%&'()*+,-./

x

x

x

0x30 .. 0x39

123456789

x

x

x

x

x

0x3a .. 0x40

:;<=>?@

x

x

x

0x41 .. 0x46

ABCDEF

x

x

x

x

x

x

0x47 .. 0x5A

GHIJKLMNOPQRSTUVWXYZ

x

x

x

x

x

0x5B .. 0x60

[\]^_`

x

x

x

0x61 .. 0x66

abcdef

x

x

x

x

x

x

0x67 .. 0x7A

ghijklmnopqrstuvwxyz

x

x

x

x

x

0x7B .. 0x7E

{|}~

x

x

x

0x7F

(DEL)

x

 转载请注明出处： http://www.cnblogs.com/double-win/ 谢谢！