[LeetCode9] Palindrome Number

最新推荐文章于 2025-11-24 14:44:53 发布

原创最新推荐文章于 2025-11-24 14:44:53 发布 · 674 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#leetcode #palindrome #回文

Leetcode 同时被 2 个专栏收录

287 篇文章

订阅专栏

LeetCode Questions

178 篇文章

订阅专栏

本文介绍了一种不使用额外空间判断整数是否为回文的方法。通过比较整数的首位数字来实现，提供了Java和C++两种语言的实现方案。

Determine whether an integer is a palindrome. Do this without extra space.

click to show spoilers.

Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

Analysis:

Each time get the first and last digit to compare.

java , only use one class variable.

public class Solution {
    int y;
	public boolean isPalindrome(int x) {
        if(x<0) return false;
		y = x;
		return check(x,y);
    }
	public boolean check(int x, int x1){
		if(x==0) return true;
		if(check(x/10, y)){
			if(x%10 == y%10){
				y/=10;
				return true;
			}else {
				return false;
			}
		}else {
			return false;
		}
	}
}

c++

bool isPalindrome(int x) {
        if(x<0) return false;
    if(x == 0) return true;
    int div = 1;
    while(x/div>=10){
        div *=10;
    }
    while(x>0){
        int r = x%10;
        int l = x/div;
        if(l!= r) return false;
        x = (x%div)/10;
        div/=100;
    }
    return true;
    }