数据结构算法之二分查找

二分查找

二分查找法实质上是不断地将有序数据集进行对半分割，并检查每个分区的中间元素。再重
复根据中间数确定目标范围并递归实行对半分割，直到中间数等于待查找的值或是目标数不在搜
索范围之内！

#include<stdio.h>
#include<Windows.h>

int int_compare(const void *key1,const void *key2){

	const int *ch1 = (const int*)key1;
	const int *ch2 = (const int*)key2;

	return (*ch1-*ch2);
}

int char_compare(const void *key1,const void *key2){
	const char *ch1 = (const char*)key1;
	const char *ch2 = (const char*)key2;

	return (*ch1-*ch2);
}
// int(compare)(const void*key1,const void*key2)比较函数传入
int searchBinary(void *sorted,int len,int Elemsize,void *search,int(compare)(const void*key1,const void*key2)){

	int left = 0;
	int right = len-1;
	int middle = 0;
	int ret = 0;

	while(left<=right){
		 middle = (right+left)/2;

		 //middle = (right-left)/2;

		//int middle = (right-left)/2  right+1就是右边移  right-1就是左移是

		ret = compare((char*)sorted+(Elemsize*middle),search);

		if(ret==0){
		return middle;//找到索引下标
		}
		
		if(ret>0){
		//middle大于要找的数
			
			right=middle-1;
			//right--;
		}
		if(ret<0){
		//middle小于要找的数
			left = middle+1;
			//right++;//这个不是二分查找了
		
		}

	}


	//否则
	return -1;//没有找到
	

}



int main(void){
	
	int arr[]={1,3,7,9,11};
	int search[]={0,-2,7,11,0,25};

	int len = sizeof(arr)/sizeof(arr[0]);
	


	for(int i=0;i<len;i++){

		int index =	searchBinary(arr,len,sizeof(int),&search[i],int_compare);
		printf("serching %d,index: %d\n",search[i],index);
	
	}


	printf("字符查找!\n");
	char ch[]={'a','b','d','e','f','s'};//按照顺序来
	char chsearch[]={'S','s','f','d','e','w','a','s','0'};

	for(int i=0;i<sizeof(chsearch)/sizeof(chsearch[0]);i++){
		
		int index = searchBinary(ch,sizeof(ch)/sizeof(ch[0]),sizeof(char),&chsearch[i],char_compare);
		printf("serching %c,index: %d\n",chsearch[i],index);

	}

	
	system("pause");
	return 0;
	}