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public class PAI
{
public static void main(String[] args)
{
int n = 700;
//Hello World! pai = 3.1401640828900845(n = 700)
System.out.println("Hello World! pai = " + getPAI(n));
//Hello World! pai = 3.1430191863875865(n = 700)
System.out.println("Hello World! pai = " + pai(n));
}
public static double getPAI(int n){
double pai = 0;
for(int i = 0;i < n;i++){
if((i&1) == 0){
pai += 4D/(2*i + 1);
}else{
pai -= 4D/(2*i + 1);
}
}
return pai;
}
public static double pai(int n){
if(n == 0){
return 4D;
}
if((n&1) == 0){
return pai(n - 1) + 4D/(2*n + 1);
}else{
return pai(n - 1) - 4D/(2*n + 1);
}
}
}
