You are given an array of strings?words. Each element of?words?consists of?two?lowercase English letters.
Create the?longest possible palindrome?by selecting some elements from?words?and concatenating them in?any order. Each element can be selected?at most once.
Return?the?length?of the longest palindrome that you can create. If it is impossible to create any palindrome, return?0.
A?palindrome?is a string that reads the same forward and backward.
Example 1:
Input: words = ["lc","cl","gg"] Output: 6 Explanation: One longest palindrome is "lc" + "gg" + "cl" = "lcggcl", of length 6. Note that "clgglc" is another longest palindrome that can be created.
Example 2:
Input: words = ["ab","ty","yt","lc","cl","ab"] Output: 8 Explanation: One longest palindrome is "ty" + "lc" + "cl" + "yt" = "tylcclyt", of length 8. Note that "lcyttycl" is another longest palindrome that can be created.
Example 3:
Input: words = ["cc","ll","xx"] Output: 2 Explanation: One longest palindrome is "cc", of length 2. Note that "ll" is another longest palindrome that can be created, and so is "xx".
Constraints:
1 <= words.length <= 105words[i].length == 2words[i]?consists of lowercase English letters.
题目链接：https://leetcode.com/problems/longest-palindrome-by-concatenating-two-letter-words/
题目大意：给一些长度为2的word，从中选若干拼接，求最长能拼出的回文串长度
题目分析：hash一下，对长度2的word最后单独再扫一便，因为可以放在最中间
17ms，时间击败95.04%
class Solution {
public int longestPalindrome(String[] words) {
int[] mp = new int[1000];
int ans = 0;
for (String word : words) {
int idx1 = word.charAt(0) - 'a';
int idx2 = word.charAt(1) - 'a';
if (idx1 != idx2) {
mp[idx1 * 26 + idx2]++;
if (mp[idx2 * 26 + idx1] > 0) {
ans += 4;
mp[idx1 * 26 + idx2]--;
mp[idx2 * 26 + idx1]--;
}
} else {
mp[idx1 * 26 + idx2]++;
if (mp[idx1 * 26 + idx2] > 1) {
mp[idx1 * 26 + idx2] -= 2;
ans += 4;
}
}
}
for (int i = 0; i < 26; i++) {
if (mp[i * 26 + i] > 0) {
ans += 2;
break;
}
}
return ans;
}
}
