HDU 5973 Game of Taking Stones (威佐夫博弈+高精度)

题意：给定两堆石子，每个人可以从任意一堆拿任意个，也可以从两堆中拿相同的数量，问谁赢。

析：直接运用威佐夫博弈，floor(abs(a, b) * (sqrt(5)+1)/2) == min(a, b) 是必败态。用java的BigDecimal，是很好用的，要十分求Sqrt(5).

代码如下：

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Scanner;

public class Main{
	public static final int maxn = 3000 + 5;

	public static void main(String []args){
		Scanner cin = new Scanner(System.in);
		BigDecimal l = new BigDecimal("2");
		BigDecimal r = new BigDecimal("3");
		BigDecimal f = new BigDecimal("5");
		BigDecimal x = l;
		for(int i = 0; i < 500; ++i){
			BigDecimal mid = l.add(r).divide(x);
			if(mid.multiply(mid).compareTo(f) < 0)  l = mid;
			else r = mid;
		}
		l = l.add(BigDecimal.ONE);

		while(cin.hasNext()){
			BigDecimal a = cin.nextBigDecimal();
			BigDecimal b = cin.nextBigDecimal();
			if(a.compareTo(b) > 0){
				BigDecimal tmp = a;
				a = b;
				b = tmp;
			}
			BigDecimal t = b.subtract(a).multiply(l).divide(BigDecimal.valueOf(2));
			BigInteger p = t.toBigInteger();
			BigInteger q = a.toBigInteger();
			if(p.equals(q))  System.out.println("0");
			else System.out.println("1");
		}
	}
}