题目描述
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
Input: "A man, a plan, a canal: Panama"
Output: true
Example 2:
Input: "race a car"
Output: false
题目思路
- 思路一、按照题目的意思，定义两个指针 ( 从后往前，从前往后 )，碰到非大小写字母或数字则忽略
class Solution {
public:
bool isPalindrome(string s) {
int i = 0;
int j = s.size() - 1;
while( i < j ){
while(i < j && ! fab(s[i])) i += 1;
while(i < j && ! fab(s[j])) j -= 1;
if(core(s[i], s[j])){
i += 1;
j -= 1;
}
else{
return false;
}
}
return true;
}
bool fab(char c){
if((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') ){
return true;
}
return false;
}
bool core(char a, char b){
if(a == b) return true;
// a 小写字母
if(a >= 'a' && a <= 'z'){
if(a -32 == b){
return true;
}
}
// a 大写字母
if(a >= 'A' && a <= 'Z'){
if(a +32 == b){
return true;
}
}
return false;
}
};
