归并排序 C++实现

归并排序是众多排序算法中的一种，它采用分治递归的方法，时间复杂度为O(nlogn),空间复杂度为O(n)。

基本思想是首先将整个区间分成两部分，分别对其进行求解，再对这两部分再次分解，直到区间分得足够小的时候进行计算，最终再合并。

#include <cstdio>
#include <cstring>
using namespace std;

void Merge(int *arry, int left, int mid, int right){
    int len1 = mid - left + 1;
    int len2 = right - mid;
    int *arry1 = new int[len1];
    int *arry2 = new int[len2];
    for(int i = 0; i < len1; i++)
        arry1[i] = arry[left + i];
    for(int i = 0; i < len2; i++)
        arry2[i] = arry[mid + 1 + i];
    int ind = left, ind1 = 0, ind2 = 0;
    while(ind1 < len1 && ind2 < len2){
        if(arry1[ind1] <= arry2[ind2])
            arry[ind++] = arry1[ind1++];
        else
            arry[ind++] = arry2[ind2++];
    }
    while(ind1 < len1)
        arry[ind++] = arry1[ind1++];
    while(ind2 < len2)
        arry[ind++] = arry2[ind2++];
    delete[] arry1;
    delete[] arry2;
}

void Merge_Sort(int *arry, int left, int right){
    if(right - left < 1)
        return;
    int mid = (left + right) / 2;
    Merge_Sort(arry, left, mid);
    Merge_Sort(arry, mid + 1, right);
    Merge(arry, left, mid, right);
}

int main()
{
    int a[] = {4, 3, 9, 10, -9, 8, 33};
    int len = sizeof(a) / sizeof(int);
    Merge_Sort(a, 0, len - 1);
    for(int i = 0; i < len; i++)
        printf("%d ", a[i]);
    printf("\n");
    return 0;
}