【Easy】125. 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.

中心思想：

从两端开始数。由于无视大小写和其它符号，先把干净的小写字符串整理出来。 注意容易错的地方： alphanumeric是指字母和数字。还有，转换成全小写字符串tmp之后，无论是字符串长度还是提取char都在tmp上处理

class Solution { public: bool isPalindrome(string s) { <span style="white-space:pre"> </span> string tmp = ""; for (int i = 0; i < n; i++){ if ((s[i] >= 'a' && s[i] <= 'z') || s[i] >= '0' && s[i] <= '9' ){ tmp += s[i]; } else if (s[i] >= 'A' && s[i] <= 'Z'){ tmp += (s[i] + 32); } } if (tmp.size() == 0 || tmp.size() == 1) return true; int left = 0; int right = tmp.size()-1; while (left < right){ if (tmp[left] != tmp[right]) return false; left++; right--; } return true; } };