Leetcode: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:
Are you consider that the string might is empty? This was a good question to ask during a interview.

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

Analysis: Test instructions to give a string, check whether it is a palindrome case. Only alphanumeric characters are considered and case-insensitive is ignored.

Note 1, consider the case that the string is empty, and use it as a palindrome

2, ignoring the difference between the case, the comparison of the case before the first conversion to a consistent

3, non-alphanumeric characters to skip, filter it, get a valid string

4, the effective string before and after the corresponding position to compare and judge

The code is as follows:

Class Solution {Public:bool isstr (char &ch) {if (ch >= ' 0 ' && ch <= ' 9 ') {R          Eturn true;          } else if (ch >= ' a ' && ch <= ' Z ') {return true;             } else if (ch >= ' A ' && ch <= ' Z ') {ch + = 32;          return true;      } return false;  } bool Ispalindrome (string s) {//Start typing your C + + solution below//do not write int          Main () function int len = s.length ();          if (len = = 0) {return true;          } string str = ""; for (int i = 0; i < len; i++) {//remove illegal char, such as "?"              "/" ... if (Isstr (S[i])) {str + = s[i];          }} len = Str.length ();          int mid = (len + 1)/2; for (int i = 0; i < mid; i++) {if (Str[i]! = str[len-1-i]) {//check front and endchar return false;      }} return true;  }  };

Other solutions:

Leetcode:valid palindrome