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    ice_elephant的博客:数据结构算法之二分查找

    作者:[db:作者] 时间:2021-09-16 15:45

    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;
    	}
    
    cs
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