Create Mergesort.cpp

Mergesort.cpp

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+// C++ program for Merge Sort
+#include <iostream>
+using namespace std;
+
+// Merges two subarrays of array[].
+// First subarray is arr[begin..mid]
+// Second subarray is arr[mid+1..end]
+void merge(int array[], int const left, int const mid,
+ int const right)
+{
+ auto const subArrayOne = mid - left + 1;
+ auto const subArrayTwo = right - mid;
+
+ // Create temp arrays
+ auto *leftArray = new int[subArrayOne],
+ *rightArray = new int[subArrayTwo];
+
+ // Copy data to temp arrays leftArray[] and rightArray[]
+ for (auto i = 0; i < subArrayOne; i++)
+ leftArray[i] = array[left + i];
+ for (auto j = 0; j < subArrayTwo; j++)
+ rightArray[j] = array[mid + 1 + j];
+
+ auto indexOfSubArrayOne
+ = 0, // Initial index of first sub-array
+ indexOfSubArrayTwo
+ = 0; // Initial index of second sub-array
+ int indexOfMergedArray
+ = left; // Initial index of merged array
+
+ // Merge the temp arrays back into array[left..right]
+ while (indexOfSubArrayOne < subArrayOne
+ && indexOfSubArrayTwo < subArrayTwo) {
+ if (leftArray[indexOfSubArrayOne]
+ <= rightArray[indexOfSubArrayTwo]) {
+ array[indexOfMergedArray]
+ = leftArray[indexOfSubArrayOne];
+ indexOfSubArrayOne++;
+ }
+ else {
+ array[indexOfMergedArray]
+ = rightArray[indexOfSubArrayTwo];
+ indexOfSubArrayTwo++;
+ }
+ indexOfMergedArray++;
+ }
+ // Copy the remaining elements of
+ // left[], if there are any
+ while (indexOfSubArrayOne < subArrayOne) {
+ array[indexOfMergedArray]
+ = leftArray[indexOfSubArrayOne];
+ indexOfSubArrayOne++;
+ indexOfMergedArray++;
+ }
+ // Copy the remaining elements of
+ // right[], if there are any
+ while (indexOfSubArrayTwo < subArrayTwo) {
+ array[indexOfMergedArray]
+ = rightArray[indexOfSubArrayTwo];
+ indexOfSubArrayTwo++;
+ indexOfMergedArray++;
+ }
+ delete[] leftArray;
+ delete[] rightArray;
+}
+
+// begin is for left index and end is
+// right index of the sub-array
+// of arr to be sorted */
+void mergeSort(int array[], int const begin, int const end)
+{
+ if (begin >= end)
+ return; // Returns recursively
+
+ auto mid = begin + (end - begin) / 2;
+ mergeSort(array, begin, mid);
+ mergeSort(array, mid + 1, end);
+ merge(array, begin, mid, end);
+}
+
+// UTILITY FUNCTIONS
+// Function to print an array
+void printArray(int A[], int size)
+{
+ for (auto i = 0; i < size; i++)
+ cout << A[i] << " ";
+}
+
+// Driver code
+int main()
+{
+ int arr[] = { 12, 11, 13, 5, 6, 7 };
+ auto arr_size = sizeof(arr) / sizeof(arr[0]);
+
+ cout << "Given array is \n";
+ printArray(arr, arr_size);
+
+ mergeSort(arr, 0, arr_size - 1);
+
+ cout << "\nSorted array is \n";
+ printArray(arr, arr_size);
+ return 0;
+}