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Count of sub-arrays whose elements can be re-arranged to form palindromes in C++
We are given an array of integer elements and the task is to calculate the count of sub-arrays that can be formed from the given array such that its elements can form a valid palindrome. Palindromes are the sequences that are arranged similarly from start and the end.
Input − int arr[] = { 3, 3, 1, 4, 2, 1, 5}
Output − Count of sub-arrays whose elements can be re-arranged to form palindromes are − 9
Explanation − The valid sub-arrays whose elements can be arranged to form a palindrome are {3}, {3}, {1}, {4}, {2}, {1}, {5}, {1, 2, 1} and {1, 3, 1}. So, the total count is 9.
Input − int arr[] = { 2, 5, 5, 2, 1}
Output − Count of sub-arrays whose elements can be re-arranged to form palindromes are − 8
Explanation − The valid sub-arrays whose elements can be arranged to form a palindrome are {2}, {5}, {5}, {2}, {1}, {5, 2, 5}, {2, 5, 2}, {2, 5, 5, 2}. So, the total count is 8.
Approach used in the below program is as follows
Input an array of integer elements and calculate the size of an array and pass the data to the function for further processing.
Declare a temporary variable count to store the sub-arrays of palindrome.
Start loop FOR from 0 till the size of an array
Inside the loop, declare a variable of type long long and set it as 1LL << arr[j] and set temp as temp ^ val
Call a function inside a boolean variable that will return either true or false.
Check IF temp is 0LL or ch is True then increment the count by 1
Return the count
Print the result.
Example
#include <bits/stdc++.h>
using namespace std;
bool check(long long temp){
return !(temp & (temp - 1LL));
}
int palindromes_rearrange(int arr[], int size){
int count = 0;
for (int i = 0; i < size; i++){
long long temp = 0LL;
for (int j = i; j < size; j++){
long long val = 1LL << arr[j];
temp = temp ^ val;
bool ch = check(temp);
if (temp == 0LL || ch){
count++;
}
}
}
return count;
}
int main(){
int arr[] = { 3, 3, 1, 4, 2, 1, 5};
int size = sizeof(arr) / sizeof(arr[0]);
cout<<"Count of sub-arrays whose elements can be re-arranged to form palindromes are:
"<<palindromes_rearrange(arr, size);
return 0;
}Output
If we run the above code it will generate the following output −
Count of sub-arrays whose elements can be re-arranged to form palindromes are: 9
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