Check whether an integer number given is palindrome or not - Leet Code Solution

September 13, 2019

Problem Statement

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:
	Input: 121
	utput: true

Example 2:
	Input: -121
	Output: false

Example 3:
	Input: 10
	Output: false

Algorithm-1

You can simply reverse the number, and compare with original number. If both are same, it is a palindrome.

Code

private int reverseInt(int x) {
	int s = 0;
	while (x > 0) {
		s = s*10 + x%10;
		x = x/10;
	}
	return s;
}

public boolean isPalindrome(int x) {
	if (x < 0) return false;
	return x == this.reverseInt(x);
}

Algorithm-2

The fastest algorithm will be one if you can compare first and last digits and move both left and right pointers inwards. So, you need a method to fetch the digit present at certain place.

Lets look at the code:

/**
 * Example: 1234
 * place=0, result=4
 * place=1, result=3
 */
private int getDigit(int x, int place) {
	x = x / (int)Math.pow(10, place);
	return x % 10;
}

public boolean isPalindrome_2(int x) {
	if (x < 0) return false;
	int l = 0;
	int temp = x;
	while (temp > 0) {
		l++;
		temp /= 10;
	}
	
	for (int i=0; i<l; i++) {
		if (this.getDigit(x, i) != this.getDigit(x, l-1-i)) {
			return false;
		}
	}
	return true;
}
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