<MEMORY>Project Euler NO.12
2014-01-21 15:11
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//三角形数序列是由对自然数的连加构造而成的。所以第七个三角形数是1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. 那么三角形数序列中的前十个是: //1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ... //下面我们列出前七个三角形数的约数: //1: 1 //3: 1,3 //6: 1,2,3,6 //10: 1,2,5,10 //15: 1,3,5,15 //21: 1,3,7,21 //28: 1,2,4,7,14,28 //可以看出28是第一个拥有超过5个约数的三角形数。 //那么第一个拥有超过500个约数的三角形数是多少? public class Problem12 { public static void main(String[] args) { long start = System.currentTimeMillis(); System.out.print("answer: "); System.out.println(TheNU()); long end = System.currentTimeMillis(); System.out.print("time: "); System.out.println(end - start); } static int TheNU() { int s = 0; for (int i = 1;;i++) { s+=i; if (isanswer(s)) { return s; } } } static boolean isanswer(int s) { int n = 0; for (int i = 1; i <= Math.sqrt(s); i++) { if (s % i == 0) { n++; } } if ( n * 2 > 500) { return true; } return false; } }
answer: 76576500 time: 690
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