05 August 2008
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
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Input: "A man, a plan, a canal: Panama"
Output: true
Example 2:
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Input: "race a car"
Output: false
判断一个字符串是否是回文字符串，忽略大小写和空格标点等，只考虑字母，难度比较小，用一下Java的api里的Character的isLetterOrDigit()和toLowerCase()/toUpperCase()方法即可。
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public class Solution {
public boolean isPalindrome(String s) {
if (s.isEmpty()) {
return true;
}
int left = 0, right = s.length() - 1;
while (left < right) {
char c1 = s.charAt(left);
char c2 = s.charAt(right);
if (!Character.isLetterOrDigit(c1)) {
left++;
} else if (!Character.isLetterOrDigit(c2)) {
right--;
} else {
if (Character.toLowerCase(c1) != Character.toLowerCase(c2)) {
return false;
}
left++;
right--;
}
}
return true;
}
}