//JHTP Exercise 5.33: Facebook User Base Growth
//by pandenghuang@163.com
/**(Facebook User Base Growth) According to CNNMoney.com, Facebook hit one billion users
in October 2012. Using the compound-growth technique you learned in Fig. 5.6 and assuming
its user base grows at a rate of 4% per month, how many months will it take for Facebook to grow
its user base to 1.5 billion users? How many months will it take for Facebook to grow its user base
to two billion users?*/public class Facebook {public static void main(String[] args){double growth_rate=0.04;double growth_rateDay=0.001333; // ~=0.04/30double base=1000000000;double target1=1500000000;double target2=2000000000;double users=0.0;int duration1=0;int duration2=0;int flagMonth=0;int durationDay1=0;int durationDay2=0;int flagDay=0;for(int i=1;i<=100;i++){users=base*Math.pow(1+growth_rate,i);if (users-target1>=0 && flagMonth==0){duration1=i;flagMonth=1;}if(users-target2>=0){duration2=i;break;}    }for(int i=1;i<=1000;i++){users=base*Math.pow(1+growth_rateDay,i);if (users-target1>=0 && flagDay==0){durationDay1=i;flagDay=1;}if(users-target2>=0){durationDay2=i;break;}   }System.out.println("2012年10月Facebook用户量达到了10亿，在此基础上，以月增长4%来预测，");System.out.printf("再过%d个月（以2012年10月为基准），Facebook用户量将超过15亿；再过%d个月，Facebook用户量将超过20亿",duration1,duration2);System.out.println("\n\n2012年10月Facebook用户量达到了10亿，在此基础上，以月增长4%（日增长约0.1333%）来预测，");System.out.printf("再过%.2f个月（以2012年10月为基准），Facebook用户量将超过15亿；再过%.2f个月，Facebook用户量将超过20亿",durationDay1/30.0,durationDay2/30.0);}
}