【大数问题】 FZU 2036 Log Calculator

用java保证精度。。。当x>=32时，在精度范围内log2(2x+1)=x。否则将a-b转化为double类型直接计算。

import java.util.Scanner;import java.math.BigInteger;import java.math.BigDecimal;import java.math.*;public class Main{public static void main(String[] args){Scanner scanner = new Scanner(System.in);BigDecimal a, b, ans, c;c = BigDecimal.valueOf(32);int t = scanner.nextInt();for(int i = 1; i <= t; i++) {a = scanner.nextBigDecimal();b = scanner.nextBigDecimal();if(a.compareTo(b) <= 0) {ans = a;a = b;b = ans;}a = a.subtract(b);if(a.compareTo(c) >= 0) ans = a.add(b);else {double tmp = Math.pow(2, a.doubleValue()) + 1;tmp = Math.log(tmp)/Math.log((double)2);ans = b.add(BigDecimal.valueOf(tmp));}ans = ans.setScale(9, BigDecimal.ROUND_HALF_UP);System.out.println("Case " + i + ": " + ans.toPlainString());}}}