diff --git a/Hashing/C++/8. Longest Chunked Palindrome Decomposition (HASHING).cpp b/Hashing/C++/8. Longest Chunked Palindrome Decomposition (HASHING).cpp new file mode 100644 index 0000000..e84f4a8 --- /dev/null +++ b/Hashing/C++/8. Longest Chunked Palindrome Decomposition (HASHING).cpp @@ -0,0 +1,111 @@ + +// Longest Chunked Palindrome Decomposition (Hashing) + +/* + +Question : We will be given a string s, and we need to split the string into small small k chunks, such that the two chunked string in positii=on opposite to one other must be same. + +Algorithm : + We will aplly rolling hash algorithm, where we will form two hash value, one for suffix substring and other for prefix substring, + and for each index we keep on checking comparing the hash values, and if they come to be same, then we unsergo further recursion with new range. + And this way we get the count of maximum no. of chunks. +*/ + + +#include +using namespace std; +# define mod 1000000007 // this is the prime number we take to generate the hash values in limited range of numbers + + +// main function defined to get the largest value of k chunks +int longest_chunked_palindrome_decomposition(string input_string, int min_index, int max_index) +{ + // condition defined to terminate the recursion at this point + if (min_index >= max_index) + { + return 0; + } + + // defined temporary variable + int x = 1; + + // now as we are using rolling hashing algorithm, we need two hash value, one for prefix substring and other for suffix substring + int substring_pre_hash = 0; + int substring_su_hash = 0; + + int i=0; + // looping through half of the loop + while(i<(max_index - min_index)/2) + { + // tempoaray variable defined to get the additinal part that we need to add to the hash value of both prefix and suffix + int temp1 = input_string[min_index + i] - 'a'; + int temp2 = input_string[max_index - i - 1] - 'a'; + + temp1 = temp1 * x; + substring_su_hash = substring_su_hash * 26; + x = (x%mod * 26)%mod; + + // now we need to generate the prefix substring hash value and the suffix substring hash value with the help of prime number defined + substring_pre_hash = (substring_pre_hash%mod + temp1%mod) % mod; + substring_su_hash = (substring_su_hash%mod + temp2%mod) % mod; + + + // after we have found the hash value for suffix and prefix, we compare both and if they came to be equal, then we go for further checkin using recursion + if (substring_pre_hash == substring_su_hash) + { + // defined the new upper and lower index for going through recursion + int min1 = min_index + i + 1; + int max1 = max_index - i - 1; + + //undergone recursion for the new value of min and max index + return longest_chunked_palindrome_decomposition(input_string, min1, max1) + 2; + } + i++; + } + + // at final if we fail to find any such chunk in the string, we return 1, as the input string cannot be divided into small chunks + return 1; +} + +int main() +{ + // declared string as input_string + string input_string; + // taking input of string + cin>>input_string; + + // decalred two variables and assigned accordingly + int min_index = 0; + int max_index = input_string.length(); + + // function called for finding the largest k chunks value after splitting + cout<<"The Maximum value of k is : "<