Palindrome Number
Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
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:
Coud you solve it without converting the integer to a string?
Solution
/**
* Palindrome Number
* @param {number} x
* @return {boolean}
* @time complexity: O(log x) because we are dividing x by 10 in each iteration
* @space complexity: O(1)
*/
function isPalindromeNumber(x) {
// Negative number and positive number with trailing zero (except zero itself)
// are not palindrome number
if(x < 0 || (x % 10 == 0 && x != 0)) {
return false;
}
let reverted = 0;
while (x > reverted) {
reverted = reverted * 10 + x % 10; // Push digits one position forward and add last digit that pop from x
x = Math.floor(x / 10); // Only keep integer, so discards decimal points
}
// When the length of x is an odd number, remove the last digit (reverted / 10)
// The middle digit doesn't matter in palindrome
return x === reverted || x === Math.floor(reverted / 10);
};
Test Case
const assert = require('chai').assert;
describe('Palindrome Number', () => {
it('should return true', () => {
assert.strictEqual(isPalindromeNumber(121), true);
});
it('should return false if it is an nagative number', () => {
assert.strictEqual(isPalindromeNumber(-123), false);
});
it('should return false if the number ends with zero', () => {
assert.strictEqual(isPalindromeNumber(10), false);
});
});
Palindrome Number
✓ should return true
✓ should return false if it is an nagative number
✓ should return false if the number ends with zero
3 passing (11ms)
