(高精度运算4.7.31)POJ 2413 How many Fibs?(大数累加)

package com.njupt.acm;

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

public class POJ_2413 {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		
		BigInteger[] fibs = new BigInteger[501];
		
		fibs[1] = new BigInteger("1");
		fibs[2] = new BigInteger("2");
		int i;
		for(i = 3 ; i < 501 ; ++i){//李先计算斐波那契数列
			fibs[i] = fibs[i-1].add(fibs[i-2]);
		}
		BigInteger zero = new BigInteger("0");
		
		while(true){
			BigInteger a = scanner.nextBigInteger();
			BigInteger b = scanner.nextBigInteger();
			
			if(a.compareTo(zero) == 0 &&  b.compareTo(zero) == 0){
				break;
			}
			
			int left = 0;
			int right = 0;
			boolean flag1 = true;
			/**
			 * 求一个区间有多少个斐波那契数,这时扫的不是区间,而是斐波那契数组
			 */
			for(i = 1 ; i < 501 ; ++i){//fib[500]就已经达到了10^100了
				if(flag1 && (fibs[i].compareTo(a) == 1 || fibs[i].compareTo(a) == 0)){
					left = i;
					flag1 = false;
				}
				
				if( fibs[i].compareTo(b) == 1 ){//需要注意对右边界的处理
					right = i;
					break;
				}
				
				if( fibs[i].compareTo(b) == 0){
					right = i+1;
					break;
				}
			}
			
			System.out.println(right - left );
		}
	}
}