C语言顺序查找&二分查找

Posted 2021-09-07 DQ_CODING

介绍

顺序查找

按照顺序一个个查找

#include<stdio.h>
//顺序查找
int search(int arr[],int len,int aim)
{
	int i;
	
	for(i=0;i<len;i++)
	{
		if(arr[i]==aim)
		{
			return i;//返回下标			
		}
	}
	return -1;//表示未查询到
	
}
int main()
{
	int arr[]={13,355,256,65,234,-1,35,-6,-3,-4,0};
	int len=sizeof(arr)/sizeof(int);//数组长度
	int id=search(arr,len,0);
	printf("查询结果:%d\\n",id);
	if(id!=-1)
	{
		printf("已找到\\n");
	}else
	{
		printf("没有找到\\n");
	}
	getchar();
	return 0;
}

二分查找

说明:
该数组必须是一个有序数组
思路:

方法1–while循环

//二分查找1--while循环
int binary1(int arr[],int len,int find)
{
	int left=0;
	int right=len-1;
	int mid=arr[(left+right)/2];
	while(left<=right)
	{
		if(find<mid)
		{
			right--;
		}else if(find>mid)
		{
			left++;
		}else if(find==mid)
		{
			return (left+right)/2;
		}
		mid=arr[(left+right)/2];
	}
	return -1;
}

方法2–递归

//二分查找2--递归
int binary2(int arr[],int left,int right,int find)
{
	int midindex=(left+right)/2;
	int mid=arr[midindex];
	if(left>right)//说明已经遍历完,未找到
	{
		return -1;
	}
	if(find<mid)
	{
		binary2(arr,left,midindex-1,find);
	}else if(find>mid)
	{
		binary2(arr,midindex+1,right,find);
	}else if(find==mid) 
	{
		return midindex;//已找到
	}
}

完整代码:

#include<stdio.h>

//二分查找1--while循环
int binary1(int arr[],int len,int find)
{
	int left=0;
	int right=len-1;
	int mid=arr[(left+right)/2];
	while(left<=right)
	{
		if(find<mid)
		{
			right--;
		}else if(find>mid)
		{
			left++;
		}else if(find==mid)
		{
			return (left+right)/2;
		}
		mid=arr[(left+right)/2];
	}
	return -1;
}


//二分查找2--递归
int binary2(int arr[],int left,int right,int find)
{
	int midindex=(left+right)/2;
	int mid=arr[midindex];
	if(left>right)//说明已经遍历完,未找到
	{
		return -1;
	}
	if(find<mid)
	{
		binary2(arr,left,midindex-1,find);
	}else if(find>mid)
	{
		binary2(arr,midindex+1,right,find);
	}else if(find==mid) 
	{
		return midindex;//已找到
	}
}


int main()
{
	int arr[]={1,2,3,6,9,10,55,100,991,1000};
	int len=sizeof(arr)/sizeof(int);
	int id1=binary1(arr,len,1000);
	int id2=binary2(arr,0,len-1,991);


	printf("方法1:\\n");
	if(id1!=-1)
	{
		printf("已找到,下标为:%d\\n",id1);
	}
	else
	{
		printf("未找到!\\n");
	}




	printf("方法2:\\n");
	if(id2!=-1)
	{
		printf("已找到,下标为:%d\\n",id2);
	}
	else
	{
		printf("未找到!\\n");
	}		
	getchar();
	return 0;
}