Check a Decimal Integer for Symmetry
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Decide whether the decimal representation of the signed integer `number` reads identically from left to right and from right to left. Return `true` when it does and `false` when it does not.
Use the integer's usual decimal notation. A minus sign is part of the representation, so negative integers do not qualify. Zero and positive single-digit integers do qualify.
### Examples
**Example 1**
```text
Input: number = 4004
Output: true
```
Reading the four digits backward produces `4004` again.
**Example 2**
```text
Input: number = -343
Output: false
```
Reversing the representation moves the minus sign to the end; it does not reproduce the original notation.
### Constraints
- `-2^31 <= number <= 2^31 - 1`
### Optional Follow-up
Can you preserve the same behavior without converting `number` to a string? This restriction applies only to the follow-up.
Overview: Check whether a signed integer reads the same in both directions in decimal notation, then consider the optional challenge of avoiding string conversion.
Community answers
Answer by Coderka14
#include
using namespace std;
class Solution {
public:
bool solution(int number) {
if (number < 0) {
return false;
}
if (number != 0 && number % 10 == 0) {
return false;
}
int reversedHalf = 0;
while (number > reversedHalf) {
int digit = number % 10;
reversedHalf = reversedHalf * 10 + digit;
number /= 10;
}
return number == reversedHalf ||
number == reversedHalf / 10;
}
};
/*
Approach: Reverse Half of the Number
Negative numbers cannot be palindromes.
Numbers ending in 0 cannot be palindromes,
except 0 itself.
Reverse only the second half of the number.
For even digits, compare both halves directly.
For odd digits, ignore the middle digit using reversedHalf / 10.
Time Complexity: O(log10(N))
Auxiliary Space: O(1)
*/