折半查找<二分查找>
折半条件：必须在一个有序数组内进行。
例如：在一个数组中查找一个数，找到就输出该元素下标，如果没找到就输出-1:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
intbin_search(int*p,intx,
int
n)
{
int
left = 0;
int
right = n - 1;
while
(left <= right)
{
int
i = 0;
i = ( right-left)/2+left;//(left&right) + ((left^right) >> 1)
//right/2+left/2;
//如果left和right很大，要防止left+right发生溢出
if
(p[i] > x)
{
right = i - 1;
}
else
if
(p[i] < x)
{
left = i + 1;
}
else
return
i;
}
return
-1;
}
intmain()
{
printf("请输入数组的大小:_"
);
int
n = 0;
scanf("%d", &n);
printf("请输入要查找的元素\n"
);
int
x = 0;
scanf("%d", &x);
int
*p = (int
*)calloc(n,
sizeof(int)); //采用动态内存，提高对内存的利用
if
(p == NULL)
{
printf("out of memory\n");
exit(1);
}
printf("请初始化数组\n"
);
for
(int
i = 0; i < n; i++)
{
scanf("%d", &p[i]);
}
int
ret=bin_search(p,x,n);
printf("%d\n", ret);
free(p);
system("pause");
return
0;
}
