归并排序

转 白话经典算法系列之五 归并排序的实现

#include <iostream>
using namespace std;

//将有二个有序数列a[first...mid]和a[mid...last]合并。  
void mergearray(int a[], int first, int mid, int last, int temp[])  
{  
	int i = first, j = mid + 1;  
	int m = mid,   n = last;  
	int k = 0;  

	while (i <= m && j <= n)  
	{  
		if (a[i] <= a[j])  
			temp[k++] = a[i++];  
		else  
			temp[k++] = a[j++];  
	}  

	while (i <= m)  
		temp[k++] = a[i++];  

	while (j <= n)  
		temp[k++] = a[j++];  

	for (i = 0; i < k; i++)  
		a[first + i] = temp[i];  
}  
void mergesort(int a[], int first, int last, int temp[])  
{  
	if (first < last)  
	{  
		int mid = (first + last) / 2;  
		mergesort(a, first, mid, temp);    //左边有序  
		mergesort(a, mid + 1, last, temp); //右边有序  
		mergearray(a, first, mid, last, temp); //再将二个有序数列合并  
	}  
}  

bool MergeSort(int a[], int n)  
{  
	int *p = new int[n];  
	if (p == NULL)  
		return false;  
	mergesort(a, 0, n - 1, p);  
	delete[] p;  
	return true;  
}  

void main()
{
	int a[] = {2, 32, 15, 29 ,1, 23, 12, 10, 5};
	MergeSort(a, sizeof(a)/sizeof(int));

	for (int i = 0; i < sizeof(a)/sizeof(int); i++)
	{
		cout << a[i] << endl;
	}
}