Package g0701_0800.s0730_count_different_palindromic_subsequences

Class Solution

java.lang.Object
g0701_0800.s0730_count_different_palindromic_subsequences.Solution
public class Solution extends Object
730 - Count Different Palindromic Subsequences.<p>Hard</p> <p>Given a string s, return <em>the number of different non-empty palindromic subsequences in</em> <code>s</code>. Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p> <p>A subsequence of a string is obtained by deleting zero or more characters from the string.</p> <p>A sequence is palindromic if it is equal to the sequence reversed.</p> <p>Two sequences <code>a<sub>1</sub>, a<sub>2</sub>, &hellip;</code> and <code>b<sub>1</sub>, b<sub>2</sub>, &hellip;</code> are different if there is some <code>i</code> for which <code>a<sub>i</sub> != b<sub>i</sub></code>.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> s = &ldquo;bccb&rdquo;</p> <p><strong>Output:</strong> 6</p> <p><strong>Explanation:</strong> The 6 different non-empty palindromic subsequences are &lsquo;b&rsquo;, &lsquo;c&rsquo;, &lsquo;bb&rsquo;, &lsquo;cc&rsquo;, &lsquo;bcb&rsquo;, &lsquo;bccb&rsquo;. Note that &lsquo;bcb&rsquo; is counted only once, even though it occurs twice.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> s = &ldquo;abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba&rdquo;</p> <p><strong>Output:</strong> 104860361</p> <p><strong>Explanation:</strong> There are 3104860382 different non-empty palindromic subsequences, which is 104860361 modulo 10<sup>9</sup> + 7.</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= s.length <= 1000</code></li> <li><code>s[i]</code> is either <code>'a'</code>, <code>'b'</code>, <code>'c'</code>, or <code>'d'</code>.</li> </ul>

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countPalindromicSubsequences

      public int countPalindromicSubsequences(String s)