二分查找.txt

#define _CRT_SECURE_NO_WARNINGS 1
//思路：利用二分查找的特点，数组内的数据是依次递增的特点，
//可以将数组中的中间地址取出来依次比较，如果要查找的数大于中间值，则必然在后半段，
//首地址就会变成middle + 1，如果要查找的小于中间值，则必然在前半段，尾部地址变成middle - 1，
//直到要查询的数与数组内的某个数相等为止。
//3种求两个平均值的方法
//z = (x + y) / 2;
//z = x + (y-x) / 2;
//z = (x&y) + ((x^y) >> 1);
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
//非递归
/*int BinarySearch(int *arr, int len,int key){
	int left = 0;
	int right = len - 1;
	assert(arr);
	assert(len > 0);
	int mid = 0;
	while (left<=right)
	{
       mid =left+((right-left)>>1);
		//mid = (left + right) / 2;
		if (*(arr + mid) > key)
		{
			right = mid - 1;

		}
	   if (*(arr + mid) < key)
		{
			left = mid + 1;

		}
		if (*(arr + mid) == key)
		{
			printf("%d在数组中,下标为%d\n",key,mid);
			break;
		}
	}
	if (left>right)
	printf("%d不在数组中\n", key);
    return 0;
}
*/
//递归
int BinarySearch(int *arr,int key,int left,int right){
	int mid = 0;
	assert(arr);
	if (left>right)
	{
		return -1;
	}
	mid = left + ((right - left) >> 1);
	if (*(arr+mid)==key)
	{
		printf("%d在数组中,下标为%d\n", key, mid);
	}
	if (*(arr + mid)> key)
	{
		BinarySearch(arr, key, left, mid-1);
	}
	if (*(arr + mid)< key)
	{
		BinarySearch(arr, key, mid+1,right);
	}
	return 0;
}
int main(){
	int arr[] = { 1, 2, 4, 5, 6, 7, 10, 13 };
	int len = sizeof(arr) / sizeof(arr[0]);
	int left = 0;
	int right = len - 1;
	int key = 0;
	printf("请输入你要查的数\n");
	scanf("%d", &key);
	//BinarySearch(arr,len,key);
	BinarySearch(arr,key,left,right);
	system("pause");
	return 0;
}