import java.util.arrays;
public class Test{
public static void printmultipicationTable(){ \\打印九九乘法表
for(int i=1;i<=9;i++)
{
for(int j=1;j<i;j++)
{
System.out.printf("%d*%d=%d\t",j,i,i*j);
}
System.out.println();
}
}
public static long factorial(int n){\\递归求阶乘
if(n==0||n==1)
return 1;
else
return n*factorial(n-1);
}
public static long factorial2(int n){\\迭代求阶乘
int r=1;
for(int i=1;i<=n;i++)
r*=i;
return r;
}
public static double calcE(int n){\\求自然对数e的值
double e=0;
for(int i=0;i<n;i++)
e+=(1.0/factorial(i));
return e;
}
public static double calcPi(int n){\\求Pi的值
double pi4=0;
for(int i=0;i<n;i++)
{
int a=2*i+1;
double b=1.0/a;
if(i%2==0)
{
pi4+=b;
}
else
{
pi4-=b;
}
}
return pi4*4;
}
public static String reverse(String s){\\字符串反转
int length=s.length();
String r="";
for(int i=length-1;i>=0;i--)
{
r+=s.charAt(i);
}
return r;
}
public static String decToHex(int n){\\将十进制转换为二进制
String r="";
while(n>0)
{
int a=n;
int b=n/16;
if(a>=10)
{
char c=(char)((a-10)+'A');
r+=c;
}
else
{
r+=a;
}
n=b;
}
return reverse(r);
}
public static void main(String[] args){
printmultipicationTable();
System.out.println(calcE(10));
System.out.println(calcPi(10000000));
System.out.println(decToHex(1958));
}
