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Valid Palindrome
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.
思路：使用start和end同时向后和向前移动，若s[start]（或者s[end]）不是数字或者字母，则继续将其向前（或者向后）移动。若某处s[start]和s[end]都是数字或者字母，且s[start]!=s[end]，则返回false。
1 class Solution { 2 public: 3 bool isPalindrome( string s ) { 4 int start = 0, end = (int)s.length()-1; 5 transform( s.begin(), s.end(), s.begin(), (int(*)(int))tolower ); 6 while( start < end ) { 7 while( start < end && !isAlphaNumerics( s[start] ) ) { ++start; } 8 while( start < end && !isAlphaNumerics( s[end] ) ) { --end; } 9 if( start < end && s[start] != s[end] ) { return false; }10 ++start; --end;11 }12 return true;13 }14 private:15 inline bool isAlphaNumerics( char achar ) {16 return ( achar >= ‘a‘ && achar <= ‘z‘ ) || ( achar >= ‘0‘ && achar <= ‘9‘ );17 }18 };
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