Easy
https://leetcode.com/problems/valid-palindrome/
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
这是一道考察回文的题目，而且是最简单的形式，即判断一个字符串是否是回文。
思路是头尾两个指针往中间对比，不过判断字符和数字的是从别处拿来用的。。
/**
* @param {string} s
* @return {boolean}
*/
var isPalindrome = function(s) {
//转为小写
s = s.toLowerCase();
let left = 0
let right = s.length - 1
while (left < right) {
if (!isValid(s[left])) {
left++;
continue;
}
if (!isValid(s[right])) {
right--;
continue;
}
if (s[left] === s[right]) {
left++;
right--;
} else {
break;
}
}
return right <= left;
};
//判断是否是合法字符（只处理数字与字符）
function isValid(c) {
const charCode = c.charCodeAt(0);
const isDigit =
charCode >= "0".charCodeAt(0) && charCode <= "9".charCodeAt(0);
const isChar = charCode >= "a".charCodeAt(0) && charCode <= "z".charCodeAt(0);
return isDigit || isChar;
}