mergesort

//
//  main.cpp
//  mergesort
//
//  Created by lingnan on 10/21/15.
//  Copyright (c) 2015 lingnan. All rights reserved.
//

#include <iostream>
using namespace std;
void merge(int arr[], int left, int mid, int right){
    int n1 = mid - left +1;
    int n2 = right - mid;
    int a1[n1], a2[n2];
    for(int i=0; i<n1; i++){
        a1[i] = arr[left+i];
    }
    for(int j=0; j<n2; j++){
        a2[j] = arr[mid+j+1];
    }
    int c_a= 0;
    int c_b = 0;
    int c = left;
    while(c_a <n1 && c_b <n2){
        if(a1[c_a] <= a2[c_b]){
            arr[c++] = a1[c_a++];
        }else{
            arr[c++] = a2[c_b++];
        }
    }
    while(c_a <n1){
        arr[c++] = a1[c_a++];
    }
    while(c_b <n2){
        arr[c++] = a2[c_b++];
    }
}

void mergesort(int arr[], int left, int right){
    if(left < right){
    int mid = (right - left)/2 + left;
    mergesort(arr, left, mid);
    mergesort(arr, mid+1, right);
    merge(arr, left, mid, right);
    }
}

void printArray(int arr[], int n){
    cout<<"The final result after mergesort is:"<<endl;
    for(int i=0; i<n;i++) {
        cout<< arr[i] <<" ";
    }
}

int main(int argc, const char * argv[]) {
    int arr[] = {3,21,5,3,2,5,3,6,454,7,3,63,4,645};
    int n = sizeof(arr)/sizeof(arr[0]);
    mergesort(arr, 0, n-1);
    printArray(arr, n);
    return 0;
}