409. Longest Palindrome

最新推荐文章于 2025-09-12 18:08:49 发布

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最新推荐文章于 2025-09-12 18:08:49 发布

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CC 4.0 BY-SA版权

文章标签： java runtime

原文链接：https://segmentfault.com/a/1190000018210785

本文介绍了一种高效算法，用于从给定的大小写敏感字符串中构建最长回文串。通过统计字符出现次数，算法能在O(n)时间内确定最长回文串长度，适用于不超过1,010个字符的输入。

Given a string which consists of lowercase or uppercase letters, find the length of the longest palindromes that can be built with those letters.
This is case sensitive, for example "Aa" is not considered a palindrome here.
Note:
Assume the length of given string will not exceed 1,010.

Example:

Input:
"abccccdd"
Output:
7
Explanation:
One longest palindrome that can be built is "dccaccd", whose length is 7.

难度：easy

题目：给定包含大小写字符组成的字符串，找出用这些字符串所能够成的最长回文串。

思路：字符统计

Runtime: 5 ms, faster than 90.61% of Java online submissions for Longest Palindrome.
Memory Usage: 34.7 MB, less than 100.00% of Java online submissions for Longest Palindrome.

class Solution {
    public int longestPalindrome(String s) {
        int[] table = new int[255];
        for (char c: s.toCharArray()) {
            table[c]++;
        }
        int length = 0, odd = 0;
        for (int i = 0; i < 255; i++) {
            if (table[i] % 2 > 0) {
                odd = 1;
            }
            
            length += table[i] - table[i] % 2;
        }
        
        return length + odd;
    }
}