归并排序c++实现

直接上代码

#include<iostream>

using namespace std;
const int SIZE = 10;

void merge_sort(int* arr,int start, int end);
void sort(int* arr, int start,int mid,int end);
void show(int* arr, int size);
int main()
{
	int arr[SIZE] = {
		1,2,7,4,3,2,9,6,7,5
	};
	merge_sort(arr, 0, 9);
	show(arr, SIZE);
	return 0;
}
void merge_sort(int* arr, int start, int end)
{
	if (start< end)
	{
		int mid = (start + end) / 2;
		merge_sort(arr,start, mid);
		merge_sort(arr, mid + 1, end);
		sort(arr, start, mid, end);
	}
}

void sort(int* arr, int start, int mid, int end)
{
	//构建两个数组AB，将要排序的两段数据放入AB中
	int lena = mid - start + 1, lenb = end - mid;
	int* A = new int[lena];
	int* B = new int[lenb];
	for (int i = 0; i < lena; i++)
	{
		A[i] = arr[start + i];
	}
	for (int  i = 0; i < lenb; i++)
	{
		B[i] = arr[mid + i+1];
	}

	//将AB两个数组进行排序
	int i = 0, j = 0;
	while (i<lena&&j<lenb)
	{
		if (A[i] > B[j])
		{
			arr[start] = A[i];
			i++;
		}
		else
		{
			arr[start] = B[j];
			j++;
		}
		start++;
	}

	//由于AB整体有序，将剩下的未排完的数据直接接到数组中排好的数据后面
	if (i < lena)
	{
		while (i<lena)
		{
			arr[start] = A[i];
			start++;
			i++;
		}
	}
	else
	{
		while (j < lenb)
		{
			arr[start] = B[j];
			start++;
			j++;
		}
	}

	//释放动态分配的内存
	delete[]A;
	delete[]B;
}
void show(int* arr, int size)
{
	for (int i = 0; i < size; i++)
	{
		cout << arr[i]<<" ";
	}
}

运行结果

思路简单介绍：递归分治