Create Count All Palindromic Subsequence.cpp

Advanced data structures/Count All Palindromic Subsequence.cpp

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+// Counts Palindromic Subsequence in a given String
+#include <cstring>
+#include <iostream>
+using namespace std;
+
+// Function return the total palindromic subsequence
+int countPS(string str)
+{
+	int N = str.length();
+
+	// create a 2D array to store the count of palindromic
+	// subsequence
+	int cps[N + 1][N + 1];
+	memset(cps, 0, sizeof(cps));
+
+	// palindromic subsequence of length 1
+	for (int i = 0; i < N; i++)
+		cps[i][i] = 1;
+
+	// check subsequence of length L is palindrome or not
+	for (int L = 2; L <= N; L++) {
+		for (int i = 0; i <= N-L; i++) {
+			int k = L + i - 1;
+			if (str[i] == str[k])
+				cps[i][k]
+					= cps[i][k - 1] + cps[i + 1][k] + 1;
+			else
+				cps[i][k] = cps[i][k - 1] + cps[i + 1][k]
+							- cps[i + 1][k - 1];
+		}
+	}
+
+	// return total palindromic subsequence
+	return cps[0][N - 1];
+}
+
+// Driver program
+int main()
+{
+	string str = "abcb";
+	cout << "Total palindromic subsequence are : "
+		<< countPS(str) << endl;
+	return 0;
+}