marge sort.cpp

#include<iostream>
using namespace std;
void merge(int arr[], int l, int mid, int r){
    int n1 = mid - l + 1;
    int n2 = r - mid;
    int a[n1];
    int b[n2];
    for (int i = 0; i < n1; i++){
        a[i] = arr[l + i];
    }
    for (int i = 0; i < n2; i++){
        b[i] = arr[mid + 1 + i];
    }
    int i = 0;
    int j = 0;
    int k = 1;
    while (i < n1 && j < n2){
        if (a[i] < b[j]){
            arr[k] = a[i];
            k++; i++;
        }
        else{
            arr[k] = b[j];
            k++; j++;
        }
    }
    while (i < n1){
        arr[k] = a[i];
        k++; i++;
    }
    while (j < n2){
        arr[k] = b[j];
        k++; j++;
    }
}
void mergeSort(int arr[], int l, int r){
    if (l < r){
        int mid = (l + r) / 2;
        mergeSort(arr, l, mid);
        mergeSort(arr, mid + 1, r);
        merge(arr, l, mid, r);
    }
}
int main(){
    int arr[]={5, 4, 3, 2, 1};
    mergeSort(arr, 0, 4);
    for(int i=0; i<5; i++){
        cout<<arr[i]<<" ";
    }
    cout<<endl;
    return 0;
}