<!--
判斷一個整數是否是迴文數。迴文數是指正序(從左向右)和倒序(從右向左)讀都是一樣的整數。
輸入: 121
輸出: true
@link: https://leetcode-cn.com/problems/palindrome-number/solution/
-->
<script>
function IsPalindrome(x){
// 特殊情況:
// 如上所述,當 x < 0 時,x 不是迴文數。
// 同樣地,如果數字的最後一位是 0,爲了使該數字爲迴文,
// 則其第一位數字也應該是 0
// 只有 0 滿足這一屬性
if(x < 0 || (x % 10 == 0 && x != 0)) {
return false;
}
let rev = 0; // reversed number
while (x >= 10) {
let cur = x % 10;
rev = rev*10 + cur;
if (x === rev) return true; // check before changing
x = ~~(x / 10); // better replace for Math.floor(), bit operator '~' inverts all the bits in your number and in the process converts the number to an int
if (x === rev) return true; // check after changing
if (x < rev) return false; // stop in case reversed number becomes greater than original value
}
return false; // the longest case (diff in the middle) // [77778777, 10004001]
}
console.log(IsPalindrome(69699696))
</script>