Palindrome Number

LeetCode 9 | Difficulty: Easy

Easy

Problem Description

Given an integer x, return true if x is a **palindrome**, and false otherwise.

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

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

Constraints:

- `-2^31 <= x <= 2^31 - 1`

Follow up: Could you solve it without converting the integer to a string?

Topics: Math

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Approach

Mathematical

Look for mathematical patterns or formulas. Consider: modular arithmetic, GCD/LCM, prime factorization, combinatorics, or geometric properties.

When to use

Problems with clear mathematical structure, counting, number properties.

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Solutions

Solution 1: C# (Best: 112 ms)

Metric	Value
Runtime	112 ms
Memory	N/A
Date	2017-07-16

Solution

public class Solution {
    public bool IsPalindrome(int x) {
    if (x < 0 || (x != 0 && x % 10 == 0))
    {
        return false;
    }
    int rev = 0;
    while (x > rev)
    {
        rev = rev*10 + x%10;
        x /= 10;            
    }
    return (x==rev || x==rev/10);
    }
}

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Complexity Analysis

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

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Interview Tips

Key Points

• Start by clarifying edge cases: empty input, single element, all duplicates.
• LeetCode provides 1 hint(s) for this problem — try solving without them first.

💡 Hints

Hint 1: Beware of overflow when you reverse the integer.