Merge Sort CPP

Sorting Algorithms/MergeSort/MergeSort.cpp

@@ -0,0 +1,188 @@
+#include <iostream>
+#include <stdlib.h>
+#include <time.h>
+
+//true for ascending and false for descending
+
+int arr_size = 10;
+
+using namespace std;
+
+// Create array and Print array used for demo purpose
+void create_array(int arr[]){
+    srand(rand()%arr_size+1*time(0));
+
+    for(int i = 0; i<arr_size; i++){
+        arr[i] = rand()%100+1;
+    }
+}
+
+void printArray(int arr[]){
+    int i;
+    for (i = 0; i < arr_size; i++)
+        cout <<arr[i] << " ";
+    cout << endl;
+}
+
+
+//Merge Sort**********************************************************************************************************
+// Merges two subarrays of arr[].
+// First subarray is arr[l...m]
+// Second subarray is arr[m+1...r]
+void merge(int arr[], int l, int m, int r, bool order) {
+    int n1 = m - l + 1;
+    int n2 = r - m;
+
+    // Create temp arrays
+    int L[n1], R[n2];
+
+    // Copy data to temp arrays L and R
+    for (int i = 0; i < n1; i++)
+        L[i] = arr[l + i];
+    for (int j = 0; j < n2; j++)
+        R[j] = arr[m + 1 + j];
+
+    // Merge the temp arrays back into arr
+
+    // Initial index of first subarray
+    int i = 0;
+
+    // Initial index of second subarray
+    int j = 0;
+
+    // Initial index of merged subarray
+    int k = l;
+
+    while (i < n1 && j < n2) {
+        //Ascending
+        if(order==true){
+            if (L[i] <= R[j]) {
+                arr[k] = L[i];
+                i++;
+            }
+            else {
+                arr[k] = R[j];
+                j++;
+            }
+            k++;
+        }
+        //Descending
+        else{
+            if (L[i] >= R[j]) {
+                arr[k] = L[i];
+                i++;
+            }
+            else {
+                arr[k] = R[j];
+                j++;
+            }
+            k++;
+        }
+    }
+
+    // Copy the remaining elements of L, if there are any
+    while (i < n1) {
+        arr[k] = L[i];
+        i++;
+        k++;
+    }
+
+    // Copy the remaining elements of R, if there are any
+    while (j < n2) {
+        arr[k] = R[j];
+        j++;
+        k++;
+    }
+}
+
+// l is for left index and r is right index of the sub-array of arr to be sorted
+void mergeSort(int arr[],int l,int r, bool order){
+    if(l>=r){
+        return;//returns recursively
+    }
+    int m =l+ (r-l)/2;
+    mergeSort(arr,l,m, order);
+    mergeSort(arr,m+1,r, order);
+    merge(arr,l,m,r,order);
+}
+
+///// Same code shorter Version
+/*
+void merge(int arr[], int l, int m, int r, bool order) {
+    int n1 = m - l + 1;
+    int n2 = r - m;
+
+    int L[n1], R[n2];
+
+    // Copy data to temp arrays L and R
+    for (int i = 0; i < n1; i++)
+        L[i] = arr[l + i];
+    for (int j = 0; j < n2; j++)
+        R[j] = arr[m + 1 + j];
+
+    int i = 0;
+    int j = 0;
+    int k = l;
+
+    while (i < n1 && j < n2) {
+        if (order ? L[i] <= R[j] : L[i] >= R[j]) {
+            arr[k] = L[i];
+            i++;
+        } else {
+            arr[k] = R[j];
+            j++;
+        }
+        k++;
+    }
+
+    while (i < n1) {
+        arr[k] = L[i];
+        i++;
+        k++;
+    }
+
+    while (j < n2) {
+        arr[k] = R[j];
+        j++;
+        k++;
+    }
+}
+
+void mergeSort(int arr[],int l,int r, bool order){
+    if (l >= r) return;
+    int m =l+ (r-l)/2;
+    mergeSort(arr,l,m, order);
+    mergeSort(arr,m+1,r, order);
+    merge(arr,l,m,r,order);
+}
+*/
+
+
+
+//Only used for demo purpose
+int main() {
+
+    int arr1[arr_size];
+
+    //Store Random integers
+    create_array(arr1);
+
+    cout<<"Unsorted Array : ";
+    printArray(arr1);
+
+
+    cout << "\nSelection Sort Ascending Order" << endl;
+    mergeSort(arr1, 0, arr_size-1, true);
+
+    cout << "Sorted Array : ";
+    printArray(arr1);
+
+
+    cout << "\nSelection Sort Descending Order" << endl;
+    mergeSort(arr1, 0, arr_size-1, false);
+
+    cout << "Sorted Array : ";
+    printArray(arr1);
+
+    return 0;
+}