Leetcode 9. Palindrome Number(判断回文数)with Javascript

題目

Leetcode 9.Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

Some hints: Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

解題思路1

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if(x < 0 || x > Math.pow(2,32)-1) return false;
    if(x < 10) return true;
    var str = ''+x;
    str = str.split('').reverse().join('');
    var num = parseInt(str);
    return num == x;
};

解題思路2

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if(x < 0 || x > Math.pow(2,32)-1) return false;
    if(x < 10) return true;
    var num = x;
    var recNum = x%10;
    x  = parseInt(x/10);
    while(x != 0){
        recNum = recNum*10;
        recNum = recNum + x%10;
        x = parseInt(x/10);
    }
    return recNum == num;
};