二分查找

#include<stdio.h>
#include<stdlib.h>

#define MAXSIZE 10
#define NotFound 0
typedef int ElementType;

typedef int Position;
typedef struct LNode *List;
struct LNode {
    ElementType Data[MAXSIZE];
    Position Last; /* 保存线性表中最后一个元素的位置 */
};

List ReadInput(); /* 裁判实现，细节不表。元素从下标1开始存储 */
Position BinarySearch( List L, ElementType X );

int main()
{
    List L;
    ElementType X;
    Position P;

    L = ReadInput();
    scanf("%d", &X);
    P = BinarySearch( L, X );
    printf("%d\n", P);

    return 0;
}

Position BinarySearch( List Tbl, ElementType K )
{
	if(Tbl==NULL)
		return NotFound;
	int low=1,high=Tbl->Last;
	int mid;
	while(low<=high)//low一定小于等于high 如下标为1、2、3 要查询的是下标为1的数,第一次是比较下标为2的,不符合 high就变成了1,如果写low<high就会返回错误的结果
	{
		mid=(low+high)/2;
		if(Tbl->Data[mid]==K)
			return mid;
		else if(Tbl->Data[mid]>K)
			high=mid-1;
		else
			low=mid+1;
	}
	return NotFound;
}