算法导论练手系列之归并排序

/*************************************************************************
    > File Name: merge-sort.c
    > Author: JayTan
    > Mail: jaytanfly@gmail.com 
    > Created Time: 2018年05月12日 星期六 09时13分18秒
 ************************************************************************/


/**MERGE的伪代码，选自算法导论 Page17
 * 功能:A是一个数组，p，q和r是数组下标，满足p=<q<r。该过程假设子数组A[p...q]和A[q+1 ...r]都已排好序。它合并这两个子数组形成单一的已排好序的子数组并代替当前的子数组A[p ..r]
 *
 * MERGE(A, p, q, r)
 *	n1 = q - p +1
 *	n2 = r -q
 *	let L[1...n1+1] and R[1...n2+1] be new arrays
 *	for i = 1 to n1
 *		L[i] = A[p+i-1]
 *	for j = 1 to n2
 *		R[j] = A[q+j]
 *
 *	L[n1 + 1] = $
 *	R[n2 + 1] = $
 *
 *	i = 1
 *	j = 1
 *	for k = p to r
 *		if L[i] =< R[j]
 *			A[k] = L[i]
 *			i++;
 *		else 
 *			A[k] = R[j]
 *			j = j+1
 *
 *然后将MERGE作为归并排序算法中的一个子程序来用。下面的过程MERGE-SORT(A, p, r)排序子数组A[p..r]中的元素。若 p => r,则该子数组最多有一个元素，所以已经排好序。否则，分解步骤简单地计算一个下标q,将A[p..r]分成两个子数组A[p..q]和A[q+1..r]，前者包含[n/2]个元素，后者包括[n/2]个元素。
 * 
 * MERGE-SORT(A, p, r)
 * if p<r
 *	q = [(p+r)/2]
 *	MERGE-SORT(A, p, q)
 *	MERGE-SORT(A, q+1, r)
 *	MERGE(A, p, q, r)
 *
 * */

#include <stdio.h>
#include <malloc.h>

void merge(int *array,int p, int q, int r);

void merge_sort(int *array,int p,int r);
int main(int argc, char** argv)
{
	int i = 0;
#if 0
	int A[] = {2,6,8,2,4,5,7,1,2,3,6};//11
	merge(A,3,6,10);
#endif

	int B[] = {3,2,54,45,12,31,36,8,6,3,87,32,62,79,26,63};
	//int B[] = {4,3,2,1};
	//int B[] = {2,1};
	printf("B before sort is:");
	for(i=0;i<sizeof(B)/sizeof(int);i++)
		printf("%d ",B[i]);
	printf("\n");

	merge_sort(B,0,sizeof(B)/sizeof(int)-1);

	printf("B after sort is:");
	for(i=0;i<sizeof(B)/sizeof(int);i++)
		printf("%d ",B[i]);
	printf("\n");

}


void merge_sort(int *array,int p,int r)
{
	int q = 0;
	if(p < r)
	{
		q = (p+r)/2;
		merge_sort(array,p,q);
		merge_sort(array,q+1,r);
		merge(array, p, q, r);
	}
}

void merge(int *array,int p, int q, int r)
{
	int n1 = q - p + 1;
	int n2 = r - q;
	int *pL = malloc((n1+1)*sizeof(int));
	int i = 0,j=0;
	int k=0;
	
	printf("array before sort is:");
	for(k=p;k<=r;k++)	
		printf("%d ",array[k]);
	printf("\n");

	for(i=0;i<n1;i++)
		pL[i] = array[p+i];
	pL[n1] = -1;
	
	for(i=0;i<n1+1;i++)
		printf("%d ",pL[i]);
	printf("\n");

	int *pR = malloc((n2+1)*sizeof(int));
	for(i=0;i<n2;i++)
		pR[i] = array[i+q+1];
	pR[n2] = -1;

	for(i=0;i<n2+1;i++)
		printf("%d ",pR[i]);
	printf("\n");

	i = 0;
	k = 0;
	
	for(k = p;k<=r;k++)
	{

		if((pL[i] <= pR[j] && pL[i] > 0)|| (pR[j] < 0) )
		{
			array[k] = pL[i];
			i++;
		}
		else
		{
			array[k] = pR[j];
			j++;
		}
	}

	printf("array after sort is:");
	for(k=p;k<=r;k++)	
		printf("%d ",array[k]);
	printf("\n");

	free(pL);
	pL = NULL;
	free(pR);
	pR = NULL;

}

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