HDU-2401-Baskets of Gold Coins

Baskets of Gold Coins

Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1626    Accepted Submission(s): 950

Problem Description

You are given N baskets of gold coins. The baskets are numbered from 1 to N. In all except one of the baskets, each gold coin weighs w grams. In the one exceptional basket, each gold coin weighs w-d grams. A wizard appears on the scene and takes 1 coin from Basket 1, 2 coins from Basket 2, and so on, up to and including N-1 coins from Basket N-1. He does not take any coins from Basket N. He weighs the selected coins and concludes which of the N baskets contains the lighter coins. Your mission is to emulate the wizard's computation. 

 

Input

The input file will consist of one or more lines; each line will contain data for one instance of the problem. More specifically, each line will contain four positive integers, separated by one blank space. The first three integers are, respectively, the numbers N, w, and d, as described above. The fourth integer is the result of weighing the selected coins. 

N will be at least 2 and not more than 8000. The value of w will be at most 30. The value of d will be less than w. 

 

Output

For each instance of the problem, your program will produce one line of output, consisting of one positive integer: the number of the basket that contains lighter coins than the other baskets. 

 

Sample Input

   
   
   
   

    
    
    
    10 25 8 1109
10 25 8 1045
8000 30 12 959879400
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    2
10
50
   
   
   
   

 

Source

ACM/ICPC 2008 Warmup（2）——测试帐号（杭州）

 

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英文不好，感谢Lover Oier的提示！
题意：有N个篮子，编号1—N，篮子中有很多金币，每个重w.但是有一个编号的篮子中，每个金币重w-d.现从第一个篮子中拿1个金币，第二个篮子中拿2个……第N-1中拿N-1个，第N中不拿，给出这些金币的总重量s，问：是第几个篮子中的金币重量较轻？
分析：一道数学题，先求1—N篮子金币应有的 总重量=w*（1+n-1)(n-1)/2, 然后求差值  差值=总重量-s ，再除以金币重量差值d则得出轻金币的个数。若为0，则必在编号N的篮子中；若不为0，得到较轻金币的个数，即为所求编号。

import java.io.*;
import java.util.*;

public class Main
{

	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);
		while (input.hasNext())
		{
			int n, w, d, s;
			n = input.nextInt();
			w = input.nextInt();
			d = input.nextInt();
			s = input.nextInt();
			int sum = 0;
			sum = w * (1 + (n - 1)) * (n - 1) / 2;
			sum = sum - s;
			d = sum / d;
			if (d == 0)
			{
				System.out.println(n);
			}
			else
			{
				System.out.println(d);
			}
		}
	}
}