9. Palindrome Number

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9. Palindrome Number

判断一个整数是否是回文数。回文数是指正序（从左向右）和倒序（从右向左）读都是一样的整数。

Example 1

Input: 121
Output: true

Example 2

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Follow up

• 你能不将整数转为字符串来解决这个问题吗？

[Tcdian]

Solution

• JavaScript Solution

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if (x === 0) {
        return true;
    }
    if (x < 0 || x % 10 === 0) {
        return false;
    }
    let reverseNum = 0;
    while(x > reverseNum) {
        reverseNum = reverseNum * 10 + x % 10;
        x = Math.floor(x / 10);
    }
    
    return x === reverseNum || x === Math.floor(reverseNum / 10);
};

• TypeScript Solution

function isPalindrome(x: number): boolean {
    if (x === 0) {
        return true;
    }
    if (x < 0 || x % 10 === 0) {
        return false;
    }
    let reverseNum = 0;
    while(x > reverseNum) {
        reverseNum = reverseNum * 10 + x % 10;
        x = Math.floor(x / 10);
    }
    
    return x === reverseNum || x === Math.floor(reverseNum / 10);
};