《c程序设计语言》-3.1 判断语句多少影响时间

#include <stdio.h>
 
#define Num 1000000
 
/*
int binsearch(int x,int v[],int n)
{
    int low,high,mid;
 
    low = 0;
    high = n-1;
 
    while(low <= high)
    {
        mid = (low + high) / 2;
 
        if(x > v[mid])
            high = mid - 1;
        else if(x < v[mid])
            low = mid + 1;
        else
            return mid;
    }
    return 0;
}
*/
 
int binsearch(int x,int c[],int n)
{
	int low = 0,high = n-1;
	int mid;
 
	mid = ( low + high ) / 2;
 
	while( low <= high && c[mid] != x )
	{
		if( c[mid] < x )
			high = mid - 1;
		else
			low = mid + 1;
		mid = ( low + high ) / 2;
	}
 
	if( c[mid] == x )
		return mid;
	return 0;
}
 
int main()
{
    int c[Num] = {0};
    int i,j = Num;
    int x = 7;
 
    for(i = 0;i < Num;i++)
    {
        c[i] = j;
        j--;
    }
    printf("%d\n",binsearch(x,c,Num));
 
    return 0;
}

亲测，第二种方法节省时间。判断语句少了，就节省时间了。