SRM154 Div.2 Easy ProfitCalculator

さっき解きました。

結構楽で10分ぐらいしかかからなかった。

stringからdoubleへの変換

問題文はコレ

PROBLEM STATEMENT
Margin is defined as the percentage of the selling price 
of an item or group of items which is profit.  For 
example, if an item costs $80 and is sold for $100, then 
there is $20 profit, or 20% margin.

You will be given a vector , items, which is all 
of the items sold in a single transaction.  Each string in 
items will be formatted as follows: "nnn.nn nnn.nn" 
(quotes for clarity), where each n is a digit between '0' 
and '9' inclusive.  Each string will be exactly 13 
characters in length.  The first number listed is the 
price the customer paid for the item.  The second number 
is what the cost to the store of the item was.

You will create a class ProfitCalculator with a method 
percent which will calculate the percentage of margin on 
the transaction and return it as an int, rounded down to 
the greatest integer less than the actual value.

For example, let's say you were given the following vector 
:
   { "012.99 008.73",
     "099.99 050.00",
     "123.45 101.07" }

The total cost is $159.80.  The total price is $236.43.  
That means $76.63 was made on this sale.  This would be a 
32.41128% margin.  Since we are rounding down, you would 
return 32.

DEFINITION
Class:ProfitCalculator
Method:percent
Parameters:vector 
Returns:int
Method signature:int percent(vector  items)


NOTES
 -The cost for some items may be greater than the price 
they was sold for.  However, the sum of the prices of all 
the items in the transaction will be greater than the sum 
of the costs of all items.


CONSTRAINTS
 -items will contain between 1 and 50 elements, inclusive.
 -Every string in items will be exactly 13 characters in 
length.
 -Every string in items will be formatted as "nnn.nn nnn.
nn" where each n is a digit between '0' and '9' inclusive, 
thus the range for each price will be between "000.00" and 
"999.99" inclusive (all quotes for clarity).
 -The total price of all items will be greater than the 
total cost of all items.
 -The total price of all items will be greater than 0.
 -The percent of margin, prior to rounding, will not be 
within 1e-5 of an integer.

なんか問題としてはSRM153とそう変わらないんですが、stringからdoubleへの変換が。。。
これにはistringstreamを使いますが、ネックはcinと使い方があまり変わらないこと。
つまりis >> x >> y;とやれば"0234.12 03453.2"がx=234.12、y=3453.2になったりするわけ。

この問題は気にしなくていいけど、あとこれの欠点はcinと同じようにdouble型の精度があらかじめ決められていること。
これもcinとおなじほうほうで解決できる。

あと注意したことはキャストを式全体に掛けているところとか、istringstreamの初期化の位置かな。
正解のコード。

class ProfitCalculator {
   public:
   int percent(vector <string> items)
  {
	double tcost=0, tprice=0, cost, price, profit;
	int ret;
	for (int i=0; i<items.size(); i++) {
		istringstream is;
		is.str(items[i]);
		is >> price >> cost;
		// cout << cost << " " << price << endl;
		tcost += cost; tprice += price;
	}
	profit = tprice - tcost;
	ret = (int)(profit/tprice*100);
	return ret;
  }
};