数据结构 PTA 顺序表 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 L, ElementType X ){
	//如果表不为空，进入指令集；如果表为空，返回notfound
	if(L == NULL)
		return NotFound;
	//如果表的只有一个元素
	if(L->Last == 1)
		return (L->Data[L->Last] != X) ? NotFound:L->Last;
	/*表的元素个数大于1
	进入查找指令集
	二分查找
	取mid = (left + right)/2
	*/
	Position lo = 1,high = L->Last;
	Position mid = (lo+high)/2;

	while (lo <= high)
	{
		if(L->Data[mid] > X)
			high = mid - 1;
		else if(L->Data[mid] < X)
			lo = mid + 1;
		else
			return mid;
		mid = (lo + high)/2;
	}
	
	return NotFound;
}