归并排序

https://www.cnblogs.com/kkun/archive/2011/11/23/2260271.html

#include<iostream>
#include <stdio.h> 
#include <stack> 

using namespace std;

void merge(int *a, int begin, int mid, int end, int * sorted_arr) {
    int i = begin;
    int j = mid;
    int k = 0;
    while (i < mid && j < end) {
        if (a[i] < a[j]) {
            sorted_arr[k] = a[i];
            k++;
            i++;
        }
        else {
            sorted_arr[k] = a[j];
            k++;
            j++;
        }
    }
    while (i < mid) {
        sorted_arr[k] = a[i];
        k++;
        i++;
    }
    while (j < end)
    {
        sorted_arr[k] = a[j];
        k++;
        j++;
    }
    for (int v =0; v < k; ++v) {
        a[begin +v] = sorted_arr[v];
    }
}

void merge_sort(int *a, int begin, int end, int * sorted_arr) {
    if (begin +1 < end) {
        
　　　　 int mid = (begin + end) / 2;

        merge_sort(a, begin, mid, sorted_arr); //假设左半部分已完成排序
        merge_sort(a, mid, end, sorted_arr); //假设右半部分已完成排序
        merge(a, begin, mid, end, sorted_arr); // 归并核心 merge
    }
    
}

int main()
{
    int a[8] = {4, 2, 6, 7, 9, 5, 1, 3};
    int length = sizeof(a) / sizeof(a[0]);

    int* sorted_arr = new int[length];
    
    merge_sort(a, 0, length, sorted_arr);
    for(int i=0; i < 8; i++) {
        cout << a[i] << " " << endl;
    }
    return 0;
}