Abstract / Summary

Determine if a given integer reads the same backward as forward.

Note

The full problem description, including helpful examples, can be found on LeetCode.

This problem is ranked as

and has an acceptance rate of about 61% (10+ million submissions).

Typical patterns to solve this problem:

• Math

Every single line of code was written by me, 100% from scratch, between August 2023 and August 2024.
However, two years later I set up this website and used various AI tools to generate most of the walkthrough / explanations below.

See this dedicated page for more details.

Overview

The provided implementation determines whether a 32-bit integer reads the same forward and backward. It follows a clear, linear flow: reject obvious non-palindromes, transform the numeric value into a textual representation, reverse that representation, and finally compare the two strings for equality.

Key Steps

Rejecting negative values

if (x < 0)
    return false;

A negative sign cannot be mirrored at the end of the number, so any negative input is immediately classified as non-palindromic. This early exit prevents further processing for values that are guaranteed to fail the palindrome test.

Converting the integer to a string

string a = to_string(x);

The integer is turned into its decimal character sequence. This step leverages the standard library conversion, which handles the full range of signed integers, including zero and the maximum positive value.

Creating a reversed copy

string b = a;
reverse(b.begin(), b.end());

A second string b is initialized as a copy of a. The std::reverse algorithm then in-place flips the order of characters, producing the mirror image of the original digit sequence.

Comparing the original and reversed strings

return a == b;

Equality of the two strings indicates that the digit order reads identically from left to right and from right to left. The boolean result of this comparison is returned directly.

Edge Cases Handled

When the input is zero, the conversion yields the string "0". Reversing this single-character string leaves it unchanged, so the comparison succeeds and the function returns true.

Single-digit positive numbers (for example, 7) also become one-character strings; the reversal does not alter them, resulting in a true outcome.

Numbers that end with a zero, such as 10 or 1200, generate strings with trailing zeros that become leading zeros after reversal ("01" or "0021"). Since the original strings lack those leading zeros, the equality test fails, correctly identifying them as non-palindromes.

Negative inputs are caught by the initial guard clause, ensuring they never reach the conversion stage.

Performance Optimizations Observed

The early return for negative numbers eliminates unnecessary work for half of the possible integer domain, saving both CPU cycles and memory allocations associated with string creation.

Using std::string and std::reverse from the standard library provides highly tuned implementations that operate directly on contiguous memory, minimizing overhead compared to manual character manipulation.

The algorithm avoids additional data structures beyond the two strings, keeping the memory footprint small and the execution path straightforward.

Imagine you have a row of colored blocks that spell out a word. A palindrome is a special kind of word that looks exactly the same whether you read it from left to right or if you turn your head around and read it from right to left.

This code acts like a little helper who checks if a number is one of these special mirrors. First, the helper looks at the number to see if it is hiding behind a minus sign. If it has a minus sign, it is not a palindrome, so the helper shakes its head no.

Next, the helper takes the number and writes it down on a piece of paper. Then, it takes a second piece of paper and writes the same number down again, but it carefully flips the order so the last number becomes the first. Finally, the helper holds both pieces of paper side by side to see if they look exactly the same. If the two papers match, then the number is a palindrome.

Several LLMs ranked my code quality on a scale from 1 (very poor) to 10 (outstanding):

not analyzed yet

I wrote a basic crawler to find other solutions to that problem.
Obviously, I did that after I solved the problem myself.

In general, AlgoMonster and WalkCCC solutions are high-quality and always worth a look.
I haven't checked most of the other solutions, but they might be helpful as well.

And of course, the LeetCode forum is always a good place (or even the best) to look for alternative approaches.

(click on a column header to sort the table)

	author
author	solutions
www	AlgoMonster	C++	Python		Java									TS
	WalkCCC	C++	Python		Java
	leetcode.ca	C++	Python	C	Java	Rust	C#	JS	Go				PHP	TS
	LeetcodeHelp	C++	Python		Java
	MemoryLimitExceeded	C++	Python
	Progiez	C++	Python		Java
github	AdelDaniel									Dart
	aylei					Rust
	begeekmyfriend			C
	BigEggStudy						C#
	black-shadows	C++
	bujosa					Rust
	chandansgowda		Python
	charles-wangkai				Java
	chenyanzhe	C++
	DimitrisJim			C
	everthis							JS
	fartem											Ruby
	fengvyi	C++
	gaosq0604		Python
	halfrost								Go
	haoel	C++
	JoshCrozier							JS
	keineahnung2345	C++
	Krazune			C
	lennylxx			C
	linouk23	C++
	lkwq007		Python
	luangong	C++
	lzl124631x	C++
	martianoff										Scala
	muhammadfarhankt								Go
	pruthvikp		Python
	qiyuangong				Java
	ruoru					Rust
	Shamik07									Dart
	shreymehul						C#
	sonugiri1043	C++
	suxrobGM						C#
	varunu28				Java
	vli02			C
	vthwang				Java
	XiaotaoGuo	C++
	YuriSpiridonov		Python
AlgoMonster	C++, Python, Java, TypeScript
WalkCCC	C++, Python, Java
leetcode.ca	C, C++, C#, Go, Java, JavaScript, PHP, Python, Rust, TypeScript
LeetcodeHelp	C++, Java, Python
MemoryLimitExceeded	Python, C++
Progiez	C++, Java, Python
AdelDaniel	Dart
aylei	Rust
begeekmyfriend	C
BigEggStudy	C#
black-shadows	C++, C++
bujosa	Rust
chandansgowda	Python
charles-wangkai	Java
chenyanzhe	C++
DimitrisJim	C
everthis	JavaScript
fartem	Ruby
fengvyi	C++
gaosq0604	Python
halfrost	Go
haoel	C++
JoshCrozier	JavaScript
keineahnung2345	C++
Krazune	C
lennylxx	C
linouk23	C++
lkwq007	Python
luangong	C++
lzl124631x	C++
martianoff	Scala
muhammadfarhankt	Go
pruthvikp	Python
qiyuangong	Java
ruoru	Rust
Shamik07	Dart
shreymehul	C#
sonugiri1043	C++
suxrobGM	C#
varunu28	Java
vli02	C
vthwang	Java
XiaotaoGuo	C++
YuriSpiridonov	Python

There are a few extra pages giving you some insights into my setup:

• Tech Stack - my development environment and tools
• AI - how AI helped me create this website (NOT solving the problems)
• Progress - progression over time
• Quality - code quality