Palindrome Number

PROBLEM

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

Example1

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

Example2

*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.

Example3

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

SOLVING

Two Pointers Method

Steps

Transform the integer to string
Add your Left Pointer to 0 and the Right Pointer to the last index
While Left Pointer is inferior to the Right Pointer:
1. If Left Element is different from Right Element, return false. The string isn’t a palindrome
Return true because we parse all the string and all character were the same

Code

class Solution {
public:
  bool isPalindrome(int x) {
    string nbStr = to_string(x);
    int leftPtr = 0;
    int rightPtr = nbStr.size() - 1;

    while (leftPtr < rightPtr) {
      if (nbStr[leftPtr] != nbStr[rightPtr])
	return false;
      leftPtr++;
      rightPtr--;
    }

    return true;
  }
};

Revert Half

Steps

Initialize var RightPart to 0 and leftPart to your number
If number is negative or number first digit is 0 return false. It can’t be a palindrome
While the RightPart is inferior to the LeftPart:
1. Add the first digit of LeftPart to RightPart by RightPart = RightPart * 10 /to add a new number/ + LeftPart % 10 /change the new number by the first digit of LeftPart/
2. Divide LeftPart by 10 to lose one digit
return the comparison between LeftPart and RightPart or LeftPart and (RightPart divided by 10)

Code

class Solution {
public:
  bool isPalindrome(int x) {
    int rightPart = 0;
    int leftPart = x;

    if (x < 0 || (x != 0 && x % 10 == 0))
      return false;

    while (rightPart < leftPart) {
      rightPart = rightPart * 10 + leftPart % 10;
      leftPart /= 10;
    }

    return leftPart == rightPart || leftPart == rightPart / 10;
  }
};

PROBLEM