p125

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LeetCode p125 Valid Palindrome 题解

1.题目：

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
“A man, a plan, a canal: Panama” is a palindrome.
“race a car” is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

题意：

只考虑数字和字母，判断一个字符串是否回文。

2.解题思路:

见代码，从两头往中间找。

3.代码

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public class Solution {
    public boolean isPalindrome(String s) {
        char[] a = s.toCharArray();
		int len = a.length;

		for (int l = 0, r = len - 1; l < r; l++, r--) {
			while (!check(a[l]) && l < r)
				l++;
			while (!check(a[r]) && l < r)
				r--;
			if (a[l] == a[r]
					|| ((a[l] < '0' || a[l] > '9') && Math.abs(a[l] - a[r]) == 32)) // 注意差值为32
				continue;

			return false;
		}
		return true;
	}

	public boolean check(char a) {
		return (a >= 'A' && a <= 'Z') || (a >= 'a' && a <= 'z')
				|| (a >= '0' && a <= '9');
	}
}

4.一些总结：