Solved problems

Author: gouthampradhan

README.md

@@ -277,6 +277,7 @@ My accepted leetcode solutions to some of the common interview problems.
 - ![#f03c15](https://placehold.it/15/f03c15/000000?text=+) [Smallest Sufficient Team](problems/src/dynamic_programming/SmallestSufficientTeam.java) (Hard)
 - ![#f03c15](https://placehold.it/15/f03c15/000000?text=+) [Stone Game IV](problems/src/dynamic_programming/StoneGameIV.java) (Hard)
 - ![#f03c15](https://placehold.it/15/f03c15/000000?text=+) [Tallest Billboard](problems/src/dynamic_programming/TallestBillboard.java) (Hard)
+- ![#f03c15](https://placehold.it/15/f03c15/000000?text=+) [Count Different Palindromic Subsequences](problems/src/dynamic_programming/CountDifferentPalindromicSubsequences.java) (Hard)
 
 
 #### [Greedy](problems/src/greedy)

problems/src/dynamic_programming/CountDifferentPalindromicSubsequences.java

@@ -2,7 +2,29 @@
 
 import java.util.Arrays;
 
-/** Created by gouthamvidyapradhan on 10/04/2021 */
+/**
+ * Created by gouthamvidyapradhan on 10/04/2021 Given a string S, find the number of different
+ * non-empty palindromic subsequences in S, and return that number modulo 10^9 + 7.
+ *
+ * <p>A subsequence of a string S is obtained by deleting 0 or more characters from S.
+ *
+ * <p>A sequence is palindromic if it is equal to the sequence reversed.
+ *
+ * <p>Two sequences A_1, A_2, ... and B_1, B_2, ... are different if there is some i for which A_i
+ * != B_i.
+ *
+ * <p>Example 1: Input: S = 'bccb' Output: 6 Explanation: The 6 different non-empty palindromic
+ * subsequences are 'b', 'c', 'bb', 'cc', 'bcb', 'bccb'. Note that 'bcb' is counted only once, even
+ * though it occurs twice. Example 2: Input: S =
+ * 'abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba' Output: 104860361 Explanation:
+ * There are 3104860382 different non-empty palindromic subsequences, which is 104860361 modulo 10^9
+ * + 7. Note:
+ *
+ * <p>The length of S will be in the range [1, 1000]. Each character S[i] will be in the set {'a',
+ * 'b', 'c', 'd'}.
+ *
+ * Solution: O(N ^ 2) x 4
+ */
 public class CountDifferentPalindromicSubsequences {
   public static void main(String[] args) {
     System.out.println(