Create partition_problem.cpp

dynamic_programming/partition_problem.cpp

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+/******************************************************************************
+ * @file
+ * @brief Implementation of the [Partition Problem](https://en.wikipedia.org/wiki/Partition_problem )
+ * @details
+ * The partition problem, or number partitioning, is the task of deciding whether
+ * a given multiset S of positive integers can be partitioned into two subsets S1
+ * and S2 such that the sum of the numbers in S1 equals the sum of the numbers in S2.
+ * Although the partition problem is NP-complete, there is a pseudo-polynomial time
+ * dynamic programming solution, and there are heuristics that solve the problem
+ * in many instances, either optimally or approximately. For this reason,
+ * it has been called "the easiest hard problem".
+ *
+ * The worst case time complexity of Jarvis’s Algorithm is O(n^2). Using
+ * Graham’s scan algorithm, we can find Convex Hull in O(nLogn) time.
+ *
+ * ### Implementation
+ *
+ * Step 1
+ * Calculate sum of the array. If sum is odd, there can not be two subsets with
+ * equal sum, so return false.
+ *
+ * Step 2
+ * If sum of array elements is even, calculate sum/2 and find a subset of array
+ * with sum equal to sum/2.
+ *
+ * @author [Lajat Manekar](https://github.com/Lazeeez)
+ *
+ *******************************************************************************/
+#include <iostream>  /// for IO Operations
+#include <vector>    /// for std::vector
+#include <numeric>   /// for std::accumulate
+
+/******************************************************************************
+ * @namespace dp
+ * @brief Dynamic programming algorithms
+ *******************************************************************************/
+namespace dp {
+
+/******************************************************************************
+ * @namespace partitionProblem
+ * @brief Partition problem algorithm
+ *******************************************************************************/
+    namespace partitionProblem {
+
+        /******************************************************************************
+         * @brief Returns true if arr can be partitioned in two subsets of equal sum,
+         * otherwise false
+         * @param arr vector containing elements
+         * @param size Size of the vector.
+         * @returns @param bool whether the vector can be partitioned or not.
+         *******************************************************************************/
+        bool findPartiion(std::vector<uint64_t> &arr, uint64_t size) {
+            uint64_t sum = std::accumulate(arr.begin() , arr.end() , 0); // Calculate sum of all elements
+
+            if (sum % 2 != 0) return false;     //if sum is odd, it cannot be divided into two equal sum
+            bool part[sum / 2 + 1];
+
+            // Initialize the part array as 0
+            for (uint64_t it = 0; it <= sum / 2; ++it) {
+                part[it] = false;
+            }
+
+            // Fill the partition table in bottom up manner
+            for (uint64_t it = 0; it < size; ++it) {
+                // The element to be included in the sum cannot be greater than the sum
+                for (uint64_t it2 = sum / 2; it2 >= arr[it]; --it2) { // Check if sum - arr[i]
+                    // ould be formed from a subset using elements before index i
+                    if (part[it2 - arr[it]] == 1 || it2 == arr[it])
+                        part[it2] = true;
+                }
+            }
+            return part[sum / 2];
+        }
+    }
+}
+
+/*******************************************************************************
+ * @brief Self-test implementations
+ * @returns void
+ *******************************************************************************/
+void test() {
+    std::vector<uint64_t> arr = {{ 1, 3, 3, 2, 3, 2 }};
+    uint64_t n = arr.size();
+    bool expected_result = true;
+    bool derived_result = dp::partitionProblem::findPartiion(arr, n);
+    std::cout << derived_result << std::endl;
+    std::cout << "1st test: ";
+    if(expected_result == derived_result) {
+        std::cout << "Passed!" << std::endl;
+    }
+    else {
+        std::cout << "Failed!" << std::endl;
+    }
+}
+
+/*******************************************************************************
+ * @brief Main function
+ * @returns 0 on exit
+ *******************************************************************************/
+int main()
+{
+    test();  // run self-test implementations
+    return 0;
+}
+