2013
12-04

# Doubles

As part of an arithmetic competency program, your students will be given randomly generated lists of from 2 to 15 unique positive integers and asked to determine how many items in each list are twice some other item in the same list. You will need a program to help you with the grading. This program should be able to scan the lists and output the correct answer for each one. For example, given the list
1 4 3 2 9 7 18 22

your program should answer 3, as 2 is twice 1, 4 is twice 2, and 18 is twice 9.

The input file will consist of one or more lists of numbers. There will be one list of numbers per line. Each list will contain from 2 to 15 unique positive integers. No integer will be larger than 99. Each line will be terminated with the integer 0, which is not considered part of the list. A line with the single number -1 will mark the end of the file. The example input below shows 3 separate lists. Some lists may not contain any doubles.

The output will consist of one line per input list, containing a count of the items that are double some other item.

1 4 3 2 9 7 18 22 0
2 4 8 10 0
7 5 11 13 1 3 0
-1 

3
2
0

mark：输入有点怪异。

# include <stdio.h>

int a[20] ;
int ans ;

int gao()
{
int i, j, n ;
int cnt = 0 ;
ans = 0 ;
while (~scanf ("%d", &n))
{
if (n == -1) return 0 ;
if (n == 0) break ;
a[cnt++] = n ;
}
for (i = 0 ; i < cnt ; i++)
{
for (j = 0 ; j < cnt ; j++)
if (a[j] == a[i]*2) ans++ ;
}
return 1 ;
}

int main ()
{
while (gao())
{
printf ("%d\n", ans) ;
}
return 0 ;
}

1. 守门员直视那个方向是两个人的间隙，而且他是往上抛的，如果非要说有意，感觉是后面那个人突然跳起来想试着挡一下发球，结果力度角度对上了球进了。而且注意球是砸后脑勺上进的，被砸的人没有主动发力，守门员要是有这技术这手感去打斯诺克分分钟世界第一，还踢球干嘛。

2. 学算法中的数据结构学到一定程度会乐此不疲的，比如其中的2－3树，类似的红黑树，我甚至可以自己写个逻辑文件系统结构来。