Merge and Quick Sort easy code

// Online C++ compiler to run C++ program online
#include <iostream>
using namespace std;
#include<bits/stdc++.h>

void swap(int *a, int *b) {
    int tmp = *a;
    *a = *b;
    *b = tmp;
}

int partition(int *arr, int p, int q) {
    int pivot = arr[p];
    int i = p;
    for(int j=p+1; j<=q; j++) {
        if(arr[j] <= pivot) {
            i++;
            swap(arr[i],arr[j]);
        }
    }
    swap(arr[i],arr[p]);
    return i;
}

void qs(int *arr, int p, int q) {
    if(p<q) {
        int m = partition(arr,p,q);
        qs(arr,p,m-1);
        qs(arr,m+1,q);
    }
}

void merge(int *arr, int s, int e) {
    int mid = (s+e)/2;
    int len1 = mid-s+1;
    int len2 = e-mid;
    int *first = new int[len1];
    int *second = new int[len2];
    // copy the values in two arrays
    int k = s;
    for(int i=0; i<len1; i++) {
        first[i] = arr[k++];
    }
    
    k = mid+1;
    for(int i=0; i<len2; i++) {
        second[i] = arr[k++];
    }
    
    int i=0, j=0;
    k = s;
    
    while(i<len1 && j<len2) {
        if(first[i] < second[j]) {
            arr[k++] = first[i++];
        }
        else {
            arr[k++] = second[j++];
        }
    }
    
    while(i<len1) {
        arr[k++] = first[i++];
    }
    
    while(j<len2) {
        arr[k++] = second[j++];
    }
    
}

void ms(int *arr, int s, int e) {
    if(s < e) {
        int mid = (s+e)/2;
        ms(arr,s,mid);
        ms(arr,mid+1,e);
        merge(arr,s,e);
    }
}

int main() {
    int n = 5;
    int arr[n] = {2,4,1,6,9};
    ms(arr,0,n-1);
    for(int i=0; i<n; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
    return 0;
}