题面
定义一个递归函数 binarySearch，使用二分查找算法查找一个整数在一个数组中的序号（这里计数从 开始）。找不到时，返回 。
假设数组中的各个元素值均不相同，且已经按升序排序。
//********** Specification of binarySearch **********
int binarySearch (int a[],int L,int R,int x);
/* PreCondition:
a is an integer array in ascending order, x is the value to be found
L and R are lower and upper bounds to be searched
PostCondition:
return position of an element of a that has value x, -1 if not found
*/
请使用提供的主程序测试你的函数，并一起提交。
#include<stdio.h>
#define N 1024
int binarySearch (int a[],int L,int R,int x)
/* PreCondition:
a is an integer array in ascending order, x is the value to be found
L and R are lower and upper bounds to be searched
PostCondition:
return position of an element of a that has value x, -1 if not found
*/
{ //TODO: your function definition
}
int main()
{ int n,i,a[N+1],x;
scanf("%d",&n);
for (i=0;i<n;i++) scanf("%d",&a[i]);
scanf("%d",&x);
//********** binarySearch is called here ***********
printf("%d\n",binarySearch(a,0,n-1,x));
//*********************************************
return 0;
}
样例
输入
7 1 3 5 7 53 355 3432 3
输出
1