mergesort.cpp

#include<iostream> 
using namespace std; 
  
// 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) 
{ 
    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[l..r] 
      
    // 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) 
    { 
        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) 
{ 
    if (l < r) 
    { 
          
        // Same as (l+r)/2, but avoids  
        // overflow for large l and h 
        int m = l + (r - l) / 2; 
  
        // Sort first and second halves 
        mergeSort(arr, l, m); 
        mergeSort(arr, m + 1, r); 
  
        merge(arr, l, m, r); 
    } 
} 
  
// UTILITY FUNCTIONS  
// Function to print an array  
void printArray(int A[], int size) 
{ 
    for(int i = 0; i < size; i++) 
        cout << A[i] << " "; 
} 
  
// Driver code 
int main() 
{ 
    int arr[] = { 12, 11, 13, 5, 6, 7 }; 
    int 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; 
}