TheAlgorithms-C-Plus-Plus/dynamic_programming/palindrome_partitioning.cpp

/**
 * @file
 * @brief Implements [Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning-ii/) algorithm, giving you the minimum number of partitions you need to make
 *
 * @details
 * palindrome partitioning uses dynamic programming and goes to all the possible partitions to find the minimum
 * you are given a string and you need to give minimum number of partitions needed to divide it into a number of palindromes
 * [Palindrome Partitioning] (https://www.geeksforgeeks.org/palindrome-partitioning-dp-17/)
 * overall time complexity O(n^2)
 * For example: example 1:-
 * String : "nitik"
 * Output : 2 => "n | iti | k"
 * For example: example 2:-
 * String : "ababbbabbababa"
 * Output : 3 => "aba | b | bbabb | ababa"
 * @author [Sujay Kaushik] (https://github.com/sujaykaushik008)
 */

#include <iostream>   // for io operations
#include <vector>     // for std::vector
#include <algorithm>  // for std::min
#include <cassert>    // for std::assert
#include <climits>    // for INT_MAX

/**
 * @namespace dynamic_programming
 * @brief Dynamic Programming algorithms
 */
namespace dynamic_programming {

    /**
     * @namespace palindrome_partitioning
     * @brief Functions for [Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning-ii/) algorithm
     */
    namespace palindrome_partitioning {

        /**
         * Function implementing palindrome partitioning algorithm using lookup table method.
         * @param str input string
         * @returns minimum number of partitions
         */
        int pal_part(const std::string &str) {

            int n = str.size();

            // creating lookup table for minimum number of cuts
            std::vector<std::vector<int> > cuts(n, std::vector<int>(n, 0));

            // creating lookup table for palindrome checking
            std::vector<std::vector<bool> > is_palindrome(n, std::vector<bool>(n, false));

            // initialization
            for (int i = 0; i < n; i++) {
                is_palindrome[i][i] = true;
                cuts[i][i] = 0;
            }

            for (int len = 2; len <= n; len++) {
                for (int start_index = 0; start_index < n - len + 1; start_index++) {

                    int end_index = start_index + len - 1;

                    if (len == 2) {
                        is_palindrome[start_index][end_index] = (str[start_index] == str[end_index]);
                    } else {
                        is_palindrome[start_index][end_index] =
                                (str[start_index] == str[end_index]) && is_palindrome[start_index + 1][end_index - 1];
                    }

                    if (is_palindrome[start_index][end_index]) {
                        cuts[start_index][end_index] = 0;
                    } else {
                        cuts[start_index][end_index] = INT_MAX;
                        for (int partition = start_index; partition <= end_index - 1; partition++) {
                            cuts[start_index][end_index] = std::min(cuts[start_index][end_index],
                                                                    cuts[start_index][partition] +
                                                                    cuts[partition + 1][end_index] + 1);
                        }
                    }
                }
            }

            return cuts[0][n - 1];
        }
    } // namespace palindrome_partitioning
}  // namespace dynamic_programming

/**
 * @brief Test Function
 * @return void
*/
static void test() {
    // custom input vector
    std::vector<std::string> custom_input{"nitik", "ababbbabbababa", "abdc"};

    // calculated output vector by pal_part Function
    std::vector<int> calculated_output(3);

    for (int i = 0; i < 3; i++) {
        calculated_output[i] = dynamic_programming::palindrome_partitioning::pal_part(custom_input[i]);
    }

    // expected output vector
    std::vector<int> expected_output{2, 3, 3};

    // Testing implementation via assert function
    // It will throw error if any of the expected test fails
    // Else it will give nothing
    for (int i = 0; i < 3; i++) {
        assert(expected_output[i] == calculated_output[i]);
    }

    std::cout << "All tests passed successfully!\n";
}

/**
 * @brief Main function
 * @returns 0 on exit
 */
int main() {
    test();  // execute the test
    return 0;
}