Scratch brush HDOJ (2) [HDOJ1001 - Sum Problem]
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Sum Problem
Time Limit: 1000/500 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
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
Author
DOOM III
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Statistic | Submit | Discuss | Note
translation
A number per line, then every other line output a number, this number is added to the input number from 1 and.
Thinking
Circulation? Is certainly not ah, because the input of each line are 32-bit. Therefore, you should use a well-known formula -
Therefore, each number can be O (1) the request.
Code
#include <iostream>
int main(int argc, char ** argv)
{
std::ios_base::sync_with_stdio(false);
long long x;
while (std::cin >> x)
std::cout << x * (x + 1) / 2 << std::endl << std::endl;
//底下就是暂停用的,不用管。
#ifdef __EDWARD_EDIT
std::cin.get();
std::cin.get();
#endif
return 0;
}