ACM书中的题目 M-13

M-13

Description
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.

Input

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.

Output

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

Sample Input

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

Sample Output

3
2
0

题目简述：
输入一组数字，输出这组数里共有多少个两倍的关系数
解题思路：
用一个数组来储存输入数据，然后再依次查找
题目细节：
输出数据以0为一组结尾，以-1为该次程序的结尾
代码：

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,a[100];
    while(1)
    {
        int sum=0;
        int i=0;
        while(cin>>n)
        {
            if(n==-1)
            return 0;
            if(n==0)
            break;
            a[i]=n;
            i++;
        }
        sort(a,a+i);
        for(int t=1;t<i;t++)
        {
            for(int q=0;q<t;q++)
            {
                if(a[t]==a[q]*2)
                sum++;
            }
        }
        cout<<sum<<endl;
    }
    return 0;
}

体会：
练习了如何输入有要求的数据，对使用while的循环更熟悉了