{"id":9418,"date":"2022-01-09T04:02:42","date_gmt":"2022-01-09T12:02:42","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=9418"},"modified":"2022-01-09T04:03:34","modified_gmt":"2022-01-09T12:03:34","slug":"leetcode-2131-longest-palindrome-by-concatenating-two-letter-words","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/hashtable\/leetcode-2131-longest-palindrome-by-concatenating-two-letter-words\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 2131. Longest Palindrome by Concatenating Two Letter Words"},"content":{"rendered":"\n

You are given an array of strings\u00a0words<\/code>. Each element of\u00a0words<\/code>\u00a0consists of\u00a0two<\/strong>\u00a0lowercase English letters.<\/p>\n\n\n\n

Create the longest possible palindrome<\/strong> by selecting some elements from words<\/code> and concatenating them in any order<\/strong>. Each element can be selected at most once<\/strong>.<\/p>\n\n\n\n

Return the length<\/strong> of the longest palindrome that you can create<\/em>. If it is impossible to create any palindrome, return 0<\/code>.<\/p>\n\n\n\n

A palindrome<\/strong> is a string that reads the same forward and backward.<\/p>\n\n\n\n

Example 1:<\/strong><\/p>\n\n\n\n

Input:<\/strong> words = [\"lc\",\"cl\",\"gg\"]\nOutput:<\/strong> 6\nExplanation:<\/strong> One longest palindrome is \"lc\" + \"gg\" + \"cl\" = \"lcggcl\", of length 6.\nNote that \"clgglc\" is another longest palindrome that can be created.\n<\/pre>\n\n\n\n
Example 2:<\/strong><\/p>\n\n\n\n
Input:<\/strong> words = [\"ab\",\"ty\",\"yt\",\"lc\",\"cl\",\"ab\"]\nOutput:<\/strong> 8\nExplanation:<\/strong> One longest palindrome is \"ty\" + \"lc\" + \"cl\" + \"yt\" = \"tylcclyt\", of length 8.\nNote that \"lcyttycl\" is another longest palindrome that can be created.\n<\/pre>\n\n\n\n
Example 3:<\/strong><\/p>\n\n\n\n
Input:<\/strong> words = [\"cc\",\"ll\",\"xx\"]\nOutput:<\/strong> 2\nExplanation:<\/strong> One longest palindrome is \"cc\", of length 2.\nNote that \"ll\" is another longest palindrome that can be created, and so is \"xx\".\n<\/pre>\n\n\n\n
Constraints:<\/strong><\/p>\n\n\n\n
  • 1 <= words.length <= 105<\/sup><\/code><\/li>
  • words[i].length == 2<\/code><\/li>
  • words[i]<\/code> consists of lowercase English letters.<\/li><\/ul>\n\n\n\n
    Solution: Match mirrored words<\/strong><\/h2>\n\n\n\n
    For any pair of mirrored words, e.g. ‘ab’ <-> ‘ba’ or ‘aa’  <-> ‘aa’, we can extend the existing longest palindrome, ans += 4.
    For any unpaired words with same letter, e.g. ‘cc’, we can only use one and put in the middle of the pladrome, ans += 2.<\/p>\n\n\n\n
    Time complexity: O(n)
    Space complexity: O(26*26)<\/p>\n\n\n\n
    \n
    C++<\/h2>\n
    \n\n
    \n\/\/ Author: Huahua\nclass Solution {\npublic:\n  int longestPalindrome(vector& words) {\n    int ans = 0;\n    int same = 0;\n    vector> m(26, vector(26));          \n    for (const string& word : words) {      \n      const int a = word[0] - 'a';\n      const int b = word[1] - 'a';\n      if (m[b][a]) {\n        --m[b][a];\n        ans += 4;\n      } else {\n        ++m[a][b];\n      }\n    }\n    for (int i = 0; i < 26; ++i)\n      if (m[i][i]) {\n        ans += 2;\n        break;\n      }\n    return ans;\n  }\n};\n<\/pre>\n<\/div><\/div>\n","protected":false},"excerpt":{"rendered":"
    You are given an array of strings\u00a0words. Each element of\u00a0words\u00a0consists of\u00a0two\u00a0lowercase English letters. Create the longest possible palindrome by selecting some elements from words and concatenating them in any order.…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[70],"tags":[82,177,95,4],"class_list":["post-9418","post","type-post","status-publish","format-standard","hentry","category-hashtable","tag-hashtable","tag-medium","tag-palindrome","tag-string","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9418","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=9418"}],"version-history":[{"count":2,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9418\/revisions"}],"predecessor-version":[{"id":9420,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9418\/revisions\/9420"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=9418"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=9418"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=9418"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}