[ACMcoder] Sum Problem

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[ACMcoder] Sum Problem

楚兴 2015-05-26 18:43:00 浏览690
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Problem Description
Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge).

In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + … + n.

Input
The input will consist of a series of integers n, one integer per line.

Output
For each case, output SUM(n) in one line, followed by a blank line. You may assume the result will be in the range of 32-bit signed integer.

Sample Input

1
100

Sample Output

1

5050

解题思路

使用公式,避免值的范围溢出

实现代码

#include <iostream>
using namespace std;

int main()
{
    int n, sum;
    while (cin>>n)
    {
        sum = (n+1)/2.0*n;
        cout<<sum<<endl<<endl;
    }
    return 0;
}

对于这道水题,也真是醉了,如下代码竟然WA:

#include <iostream>
using namespace std;

int main()
{
    int n;
    while (cin>>n)
        cout<<(n+1)/2.0*n<<endl<<endl;

    return 0;
}

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