g1701_1800.s1771_maximize_palindrome_length_from_subsequences.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g1701_1800.s1771_maximize_palindrome_length_from_subsequences;

// #Hard #String #Dynamic_Programming #2022_04_30_Time_58_ms_(87.88%)_Space_67.1_MB_(92.42%)

/**
 * 1771 - Maximize Palindrome Length From Subsequences\.
 *
 * Hard
 *
 * You are given two strings, `word1` and `word2`. You want to construct a string in the following manner:
 *
 * *   Choose some **non-empty** subsequence `subsequence1` from `word1`.
 * *   Choose some **non-empty** subsequence `subsequence2` from `word2`.
 * *   Concatenate the subsequences: `subsequence1 + subsequence2`, to make the string.
 *
 * Return _the **length** of the longest **palindrome** that can be constructed in the described manner._ If no palindromes can be constructed, return `0`.
 *
 * A **subsequence** of a string `s` is a string that can be made by deleting some (possibly none) characters from `s` without changing the order of the remaining characters.
 *
 * A **palindrome** is a string that reads the same forward as well as backward.
 *
 * **Example 1:**
 *
 * **Input:** word1 = "cacb", word2 = "cbba"
 *
 * **Output:** 5
 *
 * **Explanation:** Choose "ab" from word1 and "cba" from word2 to make "abcba", which is a palindrome.
 *
 * **Example 2:**
 *
 * **Input:** word1 = "ab", word2 = "ab"
 *
 * **Output:** 3
 *
 * **Explanation:** Choose "ab" from word1 and "a" from word2 to make "aba", which is a palindrome.
 *
 * **Example 3:**
 *
 * **Input:** word1 = "aa", word2 = "bb"
 *
 * **Output:** 0
 *
 * **Explanation:** You cannot construct a palindrome from the described method, so return 0.
 *
 * **Constraints:**
 *
 * *   `1 <= word1.length, word2.length <= 1000`
 * *   `word1` and `word2` consist of lowercase English letters.
**/
public class Solution {
    public int longestPalindrome(String word1, String word2) {
        int len1 = word1.length();
        int len2 = word2.length();
        int len = len1 + len2;
        String word = word1 + word2;
        int[][] dp = new int[len][len];
        int max = 0;
        char[] arr = word.toCharArray();
        for (int d = 1; d <= len; d++) {
            for (int i = 0; i + d - 1 < len; i++) {
                if (arr[i] == arr[i + d - 1]) {
                    dp[i][i + d - 1] =
                            d == 1 ? 1 : Math.max(dp[i + 1][i + d - 2] + 2, dp[i][i + d - 1]);
                    if (i < len1 && i + d - 1 >= len1) {
                        max = Math.max(max, dp[i][i + d - 1]);
                    }
                } else {
                    dp[i][i + d - 1] = Math.max(dp[i + 1][i + d - 1], dp[i][i + d - 2]);
                }
            }
        }
        return max;
    }
}