Update MergeSort.cpp

C++/MergeSort.cpp

@@ -1,98 +1,69 @@
-#include <iostream>
-#include <vector>
-
-using std::cout;
-using std::cin;
-using std::vector;
-
-// Merge Sort Algorithm
-
-// Time complexity
-// Best: O(n log n)
-// Average: O(n log n)
-// Worst: O(n log n)
-
-// Space complexity: O(n)
-template <class T>
-void merge(vector<T>& list, int start, int mid, int end, int &nComparisons) { // merge two sorted sublists
-    vector<T> left; // left sublist
-    vector<T> right; // right sublist
-    int leftSize = mid - start + 1; // size of left sublist
-    int rightSize = end - mid; // size of right sublist
-
-    for (int i = 0; i < leftSize; i++) { // copy left sublist to left vector
-        left.push_back(list[start+i]); // copy element
-    }
-
-    for (int i = 0; i < rightSize; i++) { // copy right sublist to right vector
-        right.push_back(list[i+mid+1]); // copy element
-    }
-
-    int pos = start; // position in list
-    int leftPos = 0; // position in left sublist
-    int rightPos = 0; // position in right sublist
-
-    while (leftPos < leftSize && rightPos < rightSize) {    // while both sublists are not empty
-        nComparisons++;    // increment comparisons
-        if (left[leftPos] < right[rightPos]) { // if left element is smaller than right element
-            list[pos] = left[leftPos]; // copy left element to list
-            leftPos++; // increment left sublist position
-        } else { // if right element is smaller than left element
-            list[pos] = right[rightPos]; // copy right element to list
-            rightPos++; // increment right sublist position
-        }
-        pos++; // increment position in list
-    }
-
-    while (leftPos < leftSize) { // while left sublist is not empty
-        list[pos] = left[leftPos]; // copy left element to list
-        leftPos++; // increment left sublist position
-        pos++; // increment position in list
-    }
-
-    while (rightPos < rightSize) { // while right sublist is not empty
-        list[pos] = right[rightPos]; // copy right element to list
-        rightPos++; // increment right sublist position
-        pos++; // increment position in list
-    }
+#include<iostream>
+using namespace std;
+void swapping(int &a, int &b) {     //swap the content of a and b
+   int temp;
+   temp = a;
+   a = b;
+   b = temp;
 }
-
-template <class T> // merge sort algorithm
-void mergeSort(vector<T>& list, int start, int end, int &nComparisons) { // sort sublist
-
-    if(end > start) { // if sublist is not empty
-        int mid = (start + end) / 2;  // find midpoint of sublist
-        mergeSort(list, start, mid, nComparisons); // sort left sublist
-        mergeSort(list, mid+1, end, nComparisons); // sort right sublist
-        merge(list, start, mid, end, nComparisons); // merge two sorted sublists
-    }
+void display(int *array, int size) {
+   for(int i = 0; i<size; i++)
+      cout << array[i] << " ";
+   cout << endl;
+}
+void merge(int *array, int l, int m, int r) {
+   int i, j, k, nl, nr;
+   //size of left and right sub-arrays
+   nl = m-l+1; nr = r-m;
+   int larr[nl], rarr[nr];
+   //fill left and right sub-arrays
+   for(i = 0; i<nl; i++)
+      larr[i] = array[l+i];
+   for(j = 0; j<nr; j++)
+      rarr[j] = array[m+1+j];
+   i = 0; j = 0; k = l;
+   //marge temp arrays to real array
+   while(i < nl && j<nr) {
+      if(larr[i] <= rarr[j]) {
+         array[k] = larr[i];
+         i++;
+      }else{
+         array[k] = rarr[j];
+         j++;
+      }
+      k++;
+   }
+   while(i<nl) {       //extra element in left array
+      array[k] = larr[i];
+      i++; k++;
+   }
+   while(j<nr) {     //extra element in right array
+      array[k] = rarr[j];
+      j++; k++;
+   }
+}
+void mergeSort(int *array, int l, int r) {
+   int m;
+   if(l < r) {
+      int m = l+(r-l)/2;
+      // Sort first and second arrays
+      mergeSort(array, l, m);
+      mergeSort(array, m+1, r);
+      merge(array, l, m, r);
+   }
+}
+int main() {
+   int n;
+   cout << "Enter the number of elements: ";
+   cin >> n;
+   int arr[n];     //create an array with given number of elements
+   cout << "Enter elements:" << endl;
+   for(int i = 0; i<n; i++) {
+      cin >> arr[i];
+   }
+   cout << "Array before Sorting: ";
+   display(arr, n);
+   mergeSort(arr, 0, n-1);     //(n-1) for last index
+   cout << "Array after Sorting: ";
+   display(arr, n);
 }
-
-
-int main()
-{
-    int nComparisons = 0;
-    vector<int> list;
-    int n;
-    cout << "Enter the number of elements in the list: ";
-    cin >> n;
-    for (int i = 0; i < n; i++) {
-        int x;
-        cout << "Enter element " << i+1 << ": ";
-        cin >> x;
-        list.push_back(x);
-    }
-    cout << "The list is: ";
-    for (int i = 0; i < n; i++) {
-        cout << list[i] << " ";
-    }
-    cout << "\n";
-    mergeSort(list, 0, n-1, nComparisons);
-    cout << "The sorted list is: ";
-    for (int i = 0; i < n; i++) {
-        cout << list[i] << " ";
-    }
-    cout << "\n";
-    cout << "The number of comparisons is: " << nComparisons << "\n";
-    return 0;
-}