Palindrome Substring Queries in C++

C++Server Side ProgrammingProgramming

In this tutorial, we need to solve palindrome substring queries of the given string. Solving palindrome substring queries is far more complex than solving regular queries in C++. It requires a far more complex code and logic.

In this tutorial, we are provided string str and Q number of substring[L...R] queries, each with two values L and R. we aim to write a program that will solve Queries to determine whether or not substring[L...R] is a palindrome. We must decide whether or not the substring formed within the range L to R is a palindrome to solve each query. For example −

Let's input "abbbabaaaba" as our input string.
The queries were [3, 13], [3, 11], [5, 8], [8, 12]
It is necessary to determine whether the substring is a plaindrome
A palindrome is "abaaabaaaba" (3, 13) .
It is not possible to write "baaa" as a palindrome [3, 11].
As in [5, 8]: "aaab" cannot be a palindrome.
There is a palindrome in "baaab" ([3, 12]).

Approach to Find the Solution

Naive Method

Here, we must find a palindrome by checking whether the substring is from index range L to R. Therefore, we need to check all the substring queries one by one and determine whether or not they are palindromes. As there are Q queries and each query takes 0(N) time to answer. It takes 0(Q.N) time in the worst case.

Example

#include <bits/stdc++.h>
using namespace std;
int isPallindrome(string str){
   int i, length;
   int flag = 0;
   length = str.length();
   for(i=0;i < length ;i++){
      if(str[i] != str[length-i-1]) {
         flag = 1; break;
      }
   }
   if (flag==1)
      return 1;
   return 0;
}
void solveAllQueries(string str, int Q, int query[][2]){
   for(int i = 0; i < Q; i++){
      isPallindrome(str.substr(query[i][0] - 1, query[i][1] - 1))? cout<<"Palindrome\n":cout<<"Not palindrome!\n";
   }
}
int main() {
   string str = "abccbeba"; int Q = 3;
   int query[Q][2] = {{3, 5}, {5, 7}, {2, 1}};
   solveAllQueries(str, Q, query);
   return 0;
}

Output

Palindrome
Palindrome
Not palindrome!

Dynamic Programming Method

Using a dynamic programming approach to solve the problem is an efficient option. To solve, we'll need to make a DP array, which is a two-dimensional array that contains a boolean value indicating if the substring[i...j] is a palindrome for DP[i][j].

This DP matrix will be created, and all L-R values for each query will be checked.

Example

#include <bits/stdc++.h>
using namespace std;
void computeDP(int DP[][50], string str){
   int length = str.size();
   int i, j;
   for (i = 0; i < length; i++) {
      for (j = 0; j < length; j++)
         DP[i][j] = 0;
   }
   for (j = 1; j <= length; j++) {
      for (i = 0; i <= length - j; i++) {
         if (j <= 2) {
            if (str[i] == str[i + j - 1])
               DP[i][i + j - 1] = 1;
         }
         else if (str[i] == str[i + j - 1])
            DP[i][i + j - 1] = DP[i + 1][i + j - 2];
      }
   }
}
void solveAllQueries(string str, int Q, int query[][2]){
   int DP[50][50];
   computeDP(DP, str);
   for(int i = 0; i < Q; i++){
      DP[query[i][0] - 1][query[i][1] - 1]?cout
      <<"not palindrome!\n":cout<<"palindrome!\n";
   }
}
int main() {
   string str = "abccbeba"; int Q = 3;
   int query[Q][2] = {{3, 5}, {5, 7}, {2, 1}};
   solveAllQueries(str, Q, query);
   return 0;
}

Output

palindrome!
not palindrome!
palindrome!

Conclusion

In this tutorial, we learned how to solve palindrome substring queries along with the c++ code. We can also write this code in java, python, and other languages. This code was one of the most complex and lengthy codes. Palindrome queries are harder than regular substring queries, and they require very accurate logic. We hope you find this tutorial helpful.

raja
Updated on 07-Mar-2022 07:59:03

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