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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.
给定一个字符串，仅仅关注英文字母和数字，忽略其它字符。问英文字母和数字按序排列后是否构成是回文
class Solution {
public:
bool isAlphanumeric(char c){
if(isdigit(c))return true;
if(c>='A'&&c<='Z'||c>='a'&&c<='z')return true;
return false;
}
bool isEqual(char c, char b){
if(isdigit(c))return c==b;
if(c>='A'&&c<='Z')c='a'+(c-'A');
if(b>='A'&&b<='Z')b='a'+(b-'A');
return c==b;
}
bool isPalindrome(string s) {
int len=s.length();
if(len==0)return true;
int front=0;
int back=len-1;
while(front<back){
while(front<=back && !isAlphanumeric(s[front]))front++;
while(front<=back && !isAlphanumeric(s[back]))back--;
if(front<=back){
if(!isEqual(s[front], s[back]))return false;
front++;
back--;
}
}
return true;
}
};LeetCode: Valid Palindrome [125]
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原文地址：http://www.cnblogs.com/yxwkf/p/4552310.html
