Problem 9
问题描述：
A Pythagorean triplet is a set of three natural numbers, a b c, for which,

a2 + b2 = c2
For example, 32 + 42 = 9 + 16 = 25 = 52.

There exists exactly one Pythagorean triplet for which a + b + c = 1000.
Find the product abc.

通过条件可以限制a,b的范围

public static String count(){StringBuffer s = new StringBuffer();for(int a=1 ; a<400; a++){for(int b=a+1; b<500 ; b++){int c = 1000-a-b;if(a*a+b*b==c*c){int r = a*b*c;s.append(r);}}}return s.toString();}