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Queries to check if substring[L…R] is palindrome or not in C++ Program
In this problem, we are given string str, Q number of queries each consisting of two values L and R for substring[L...R]. Our task is to create a program to solve Queries to check if substring[L…R] is palindrome or not.
Problem Description − For solving each query, we need to check whether the substring created within the range L to R is a palindrome or not.
Let’s take an example to understand the problem,
Input
str = “abccbeba” , Q = 3
Query[][] = {{1, 4}, {0, 6}, {4, 6}}Output
Palindrome Not Palindrome Palindrome
Explanation
Creating all substring for the given substrings : Substring[1...4] = “bccb”, it is a palindrome Substring[0...6] = “abccbeb”, it is a not palindrome Substring[4...6] = “beb”, it is a palindrome
Solution Approach
A simple solution to the problem is to solve each query. To solve it, we need to find the substring from index range L to R. And check if the substring is a palindrome or not.
Program to illustrate the working of our solution,
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] = {{1, 3}, {2, 5}, {4, 5}};
solveAllQueries(str, Q, query);
return 0;
}Output
Palindrome Not palindrome! Palindrome
This is a naive approach but is not an efficient one.
An efficient solution to the problem is using dynamic programming approach. For solving, we need to create a DP array a 2-D array that stores a boolean value that denotes whether the substring[i...j] is a palindrome for DP[i][j].
We will create this DP matrix and check for all L-R values of each query.
Program to illustrate the working of our solution,
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] = {{1, 3}, {2, 5}, {4, 5}};
solveAllQueries(str, Q, query);
return 0;
}Output
palindrome! not palindrome! palindrome!
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