題目

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.

分析

題目給出一個字符串，判斷該字符串是不是回文，但是要忽略除了數(shù)字字母以外的任何字符，并且不區(qū)分大小寫，而且有空字符串的情況出現(xiàn)，空字符串判定為真

解題的想法就是，先得到干凈的字符串（只有字母數(shù)字），然后首位開始依次向中間移動開始判斷

代碼

class Solution {
public:
    bool isPalindrome(string s) {
        //判斷字符串是不是為空，為空直接true 
        if(s.empty()) 
            return true;
        //去除除了字母和數(shù)字以外的所有字符 
        string str = clear(s);

        for (int i=0,j=str.length()-1;i<j;i++,j--){
            if (str[i]!=str[j]){
                return false;
            }
        }
        
        return true; 
    }
    
    //清理函數(shù)，將字符串去除除了字母和數(shù)字意外的字符，并將全部字符轉(zhuǎn)為小寫 
    string clear(string s){
        string str = "";
        char c;
        for(int i=0;i<s.length();i++){
            c = s[i];
            if (c>='A'&&c<='Z' || c>='a'&&c<='z' || c>='0'&&c<='9'){
                if (c>='A'&c<='Z')
                    str+=c+32;
                else
                    str+=c;
            }
        } 
        return str;
    } 
};