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| 1 | +package dynamic_programming; |
| 2 | + |
| 3 | +import java.util.Arrays; |
| 4 | + |
| 5 | +/** Created by gouthamvidyapradhan on 10/04/2021 */ |
| 6 | +public class CountDifferentPalindromicSubsequences { |
| 7 | + public static void main(String[] args) { |
| 8 | + System.out.println( |
| 9 | + new CountDifferentPalindromicSubsequences() |
| 10 | + .countPalindromicSubsequences( |
| 11 | + "abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba")); |
| 12 | + } |
| 13 | + |
| 14 | + private long[][][] DP; |
| 15 | + final char[] chars = {'a', 'b', 'c', 'd'}; |
| 16 | + final int MOD = (int) 1e9 + 7; |
| 17 | + |
| 18 | + public int countPalindromicSubsequences(String S) { |
| 19 | + DP = new long[S.length()][S.length()][4]; |
| 20 | + for (int i = 0; i < S.length(); i++) { |
| 21 | + for (int j = 0; j < S.length(); j++) { |
| 22 | + Arrays.fill(DP[i][j], -1); |
| 23 | + } |
| 24 | + } |
| 25 | + long result = 0L; |
| 26 | + for (char c : chars) { |
| 27 | + long r = dp(0, S.length() - 1, S, c); |
| 28 | + result = ((result + r) % MOD); |
| 29 | + } |
| 30 | + return (int) result; |
| 31 | + } |
| 32 | + |
| 33 | + private long dp(int i, int j, String s, char c) { |
| 34 | + if (i > j) return 0; |
| 35 | + else if (DP[i][j][c - 'a'] != -1) return DP[i][j][c - 'a']; |
| 36 | + else if (s.charAt(i) == s.charAt(j) && s.charAt(i) == c) { |
| 37 | + if (i == j) return 1; |
| 38 | + else { |
| 39 | + long sum = 0L; |
| 40 | + for (char aChar : chars) { |
| 41 | + long r = dp(i + 1, j - 1, s, aChar); |
| 42 | + if (aChar == c) { |
| 43 | + r = ((r + 2) % MOD); |
| 44 | + } |
| 45 | + sum = ((sum + r) % MOD); |
| 46 | + } |
| 47 | + DP[i][j][c - 'a'] = sum; |
| 48 | + return DP[i][j][c - 'a']; |
| 49 | + } |
| 50 | + } else if (s.charAt(i) == c) { |
| 51 | + DP[i][j][c - 'a'] = dp(i, j - 1, s, c); |
| 52 | + return DP[i][j][c - 'a']; |
| 53 | + } else if (s.charAt(j) == c) { |
| 54 | + DP[i][j][c - 'a'] = dp(i + 1, j, s, c); |
| 55 | + return DP[i][j][c - 'a']; |
| 56 | + } else { |
| 57 | + DP[i][j][c - 'a'] = dp(i + 1, j - 1, s, c); |
| 58 | + return DP[i][j][c - 'a']; |
| 59 | + } |
| 60 | + } |
| 61 | +} |
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