Palindrome Number

最新推荐文章于 2024-10-27 22:09:20 发布

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最新推荐文章于 2024-10-27 22:09:20 发布

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本文介绍了一种不使用额外空间来判断整数是否为回文数的方法，包括处理负数、反转整数以及解决溢出问题的策略。

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

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.

public class Solution {
    public boolean isPalindrome(int x) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(x < 0)
            return false;
        int div = 1;
        while(x / div >= 10){
            div = div * 10;
        }
        while(x != 0){
            int left = x / div;
            int right = x % 10;
            if(left != right)
                return false;
            x = (x % div) / 10;
            div /= 100;
        }
        return true;
    }
}

Recursive Solution

public class Solution {
    public int y;
	public boolean isPalindrome_helper(int x){
		if(x < 0)
			return false;
		if(x == 0) return true;
		if(isPalindrome_helper(x / 10) && (x % 10 == y % 10)){
			y /= 10;
			return true;
		} else {
			return false;
		}
	}
	public boolean isPalindrome(int x){
		// Start typing your Java solution below
		// DO NOT write main() function
		y = x;
		return isPalindrome_helper(x);
	}
}