C程序设计语言 Exercise 3-1

Exercise 3-1. Our binary search makes two tests inside the loop, when one would suffice (at

the price of more tests outside.) Write a version with only one test inside the loop and

measure the difference in run-time.

#include "stdio.h"
#include "time.h"
#define MAX_LENGTH 2000000

int BinSearch1(int,int[],int);
int BinSearch2(int,int[],int);

int
main(){
int v[MAX_LENGTH] = {0};
int i = 0;

for (i = 0;i < MAX_LENGTH;i++) {
v[i] = i;
}

clock_t stStartTime = clock();
for (i = 0;i < MAX_LENGTH;i++) {
BinSearch1(i,v,sizeof(v)/sizeof(*v));
}
printf("BinSearch1==>%f\n",((double)(clock() - stStartTime)) / CLOCKS_PER_SEC);

stStartTime = clock();
for (i = 0;i < MAX_LENGTH;i++) {
BinSearch2(i,v,sizeof(v)/sizeof(*v));
}
printf("BinSearch2==>%f\n",((double)(clock() - stStartTime)) / CLOCKS_PER_SEC);
return 0;
}

int
BinSearch1(int x,int v[],int n)
{
int start = 0;
int end = n - 1;
int middle = 0;

while(start <= end) {
middle = (start + end) / 2;
if(v[middle] < x) {
start = middle + 1;
}
else if(v[middle] > x){
end = middle - 1;
}
else {
return middle;
}
}
return -1;
}

int
BinSearch2(int x,int v[],int n){
int start = 0;
int end = n - 1;
int middle = 0;
while(start <= end && v[middle] != x){
middle = (start + end) / 2;
if(v[middle] < x) {
start = middle + 1;
}
else{
end = middle - 1;
}
}
return v[middle] == x ? middle: -1;
}