H面试程序（18）： 归并排序

 

#include<stdio.h>
#include<malloc.h>
void copyArray(int source[], int dest[],int len,int first);
void merge(int a[],int left,int right);

void show_array( int a[], int n )
{
    int i;
    for( i = 0; i < n; i++ )
        printf( "%d ", a[i] );
	printf("\n");
}

void mergeSort(int a[],int left,int right)
{
	int i;
	// 保证至少有两个元素
	if(left < right)
	{
		i = (left+right)/2;
		mergeSort(a,left,i);
		mergeSort(a,i+1,right);
		merge(a,left,right);
	}
}

void merge(int a[],int left,int right)
{
	int begin1 = left;
	int mid = (left+right)/2 ;
	int begin2 = mid+1;
	int k=0;
	int newArrayLen = right-left+1;
	int *b = (int*)malloc(newArrayLen*sizeof(int));
	while(begin1<=mid && begin2<=right)
	{
		if(a[begin1]<=a[begin2])
			b[k++] = a[begin1++];
		else
			b[k++] = a[begin2++];
	}
	while(begin1<=mid)
		b[k++] = a[begin1++];
	while(begin2<=right)
		b[k++] = a[begin2++];
	copyArray(b,a,newArrayLen,left);
	free(b);
}

/**
 * 复制数组
 * source:源数组
 * dest:目标数组
 * len:源数组长度
 * first:目标数组起始位置
 *
 */

void copyArray(int source[], int dest[],int len,int first)
{
	int i;
	int j=first;
	for(i=0;i<len;i++)
	{
		dest[j] = source[i];
		j++;
	}
		
}
int main()
{
	int a[] = {2,1,3,6,4,5,7,10,8,9,2,5};
	int len = sizeof(a)/sizeof(int);
	show_array(a,len);
	mergeSort(a,0,len-1);	
	show_array(a,len);
	return 0;
}