数据结构笔记--1.1.3关于算法效率 计算多项式值

秦九韶算法

clock() 计时函数的用法

#include "stdafx.h"
#include <iostream>
#include <time.h>

clock_t start, stop;
double duration;

int main()
{
start = clock();
//myfunction();
stop = clock();
duration = ((double)(stop - start)) / CLK_TCK;
std::cout<<duration;
return 0;
}

普通方法和秦九韶算法

#include "stdafx.h"
#include <iostream>
#include <time.h>
#include <math.h>
#define MAXK 1e7 //被测函数最大重复调用次数10的7次方
#define MAXN 10
double f1(int n, double a[], double x);
double f2(int n, double a[], double x);
clock_t start, stop;
double duration = 0.0;

double f1(int n, double a[], double x)
{
int i;
double p = a[0];
for (i = 1;i <=n;i++)
p += (a[i] * pow(x, i));
//std::cout << p;
//std::cout << std::endl;
return p;
}

double f2(int n, double a[], double x)
{
int i;
double p = a
;
for (i = n;i > 0;i--)
p = a[i-1] + p*x;//i-1
//std::cout << p;
//std::cout << std::endl;
return p;
}

int main()
{
int i;
double a[MAXN];
for (i = 0;i < MAXN;i++)
a[i] = (double)i;

start = clock();
//myfunction();
for (i = 0;i < MAXK;i++)
f1(MAXN - 1, a, 1.1);
stop = clock();
duration = ((double)(stop - start)) / CLK_TCK/MAXK;
std::cout << "1=" << ((double)(stop - start));
std::cout << std::endl;
std::cout <<"1="<< duration;
std::cout << std::endl;

start = clock();
//myfunction();
for (i = 0;i < MAXK;i++)
f2(MAXN - 1, a, 1.1);
stop = clock();
duration = ((double)(stop - start)) / CLK_TCK/MAXK;
std::cout << "2=" << ((double)(stop - start));
std::cout << std::endl;
std::cout << "2="<<duration;
return 0;
}