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 2000000int BinSearch1(int,int[],int);int BinSearch2(int,int[],int);intmain(){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;}intBinSearch1(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;}intBinSearch2(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;}