归并排序的一种c++实现

1. 归并排序介绍

    归并排序的原则是分治法，里面有递归和合并的概念，时间复杂度是O（nlgn）。

2. 归并排序的实现

#include <iostream>
#include <vector>

using namespace std;

void inputNumbers(vector<int> &arrays){
    cout<<"Please input numbers:";
    int num;
    while(cin>>num){
        arrays.push_back(num);
    }
    cout<<endl;
}

void mergeSortImpl(vector<int>&arrays, int begin, int end);
void mergeSort(vector<int> &arrays){
   mergeSortImpl(arrays, 0, arrays.size()-1); 
}

void outputNumbers(const vector<int> &arrays){
    cout<<"The sorted nubers: ";
    for(vector<int>::const_iterator iter=arrays.begin(); iter!=arrays.end(); ++iter)
        cout<<*iter<<" ";

    cout<<endl;
}

void mergeTwo(vector<int> &arrays, int begin, int middle, int end){
    int array1[middle - begin + 1];
    int array2[end - middle];
    
    int index=0;
    for(int i=begin; i!=(middle+1); ++i)
        array1[index++] = arrays[i];

    index = 0;
    for(int i=middle+1; i!=end+1; ++i)
        array2[index++] = arrays[i];

    int i = 0;
    int j = 0;
    int k = begin;
    while(i!=middle-begin+1 && j!=end-middle){
        arrays[k] = array1[i]<array2[j]?array1[i++]:array2[j++];
        ++k;
    }
    
    while(i!=middle-begin+1)
        arrays[k++] = array1[i++];
    
    while(j!=end-middle)
        arrays[k++] = array2[j++];
}

void mergeSortImpl(vector<int>&arrays, int begin, int end){
   if(begin < end){
        int middle = (begin + end)/2;
        mergeSortImpl(arrays, begin, middle);
        mergeSortImpl(arrays, middle+1, end);
        mergeTwo(arrays, begin, middle, end);
    } 
}

int main(){
    vector<int> arrays; 

    //input numbers
    inputNumbers(arrays);

    //mergesort
    mergeSort(arrays);

    //output numbers 
    outputNumbers(arrays);

    return 0;
}

3. 测试

    Please input numbers:12 34 56 11 22 33 689 321
    The sorted nubers: 11 12 22 33 34 56 321 689