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。

 class Solution {
public:
bool isPalindrome(string s) {
int left=,right =s.size()-;
while(left<right)
{
if(!isalnum(s[left]))
left++;
else if(!isalnum(s[right]))
right--;
else
{
if(tolower(s[left])==tolower(s[right]))
{
left++;
right--;
}
else
return false;
}
}
return true;
}
};

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!

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