Blue Bridge Cup 3 sequence summation

Entry training Sum a sequence  

The time limit ：1.0s   Memory limit ：256.0MB

   

Problem description

seek 1+2+3+...+n Value .

Input format

Input includes an integer n.

Output format

Output one line , Include an integer , Express 1+2+3+...+n Value .

The sample input

4

Sample output

10

The sample input

100

explain ： There are some test questions that give multiple sets of sample input and output to help you do better .

Generally, all these samples need to pass the test before they are submitted , But it doesn't mean that these groups of sample data are correct, and your program is completely correct , Potential mistakes may still lead to lower scores .

Sample output

5050

Data scale and agreement

1 <= n <= 1,000,000,000.

explain ： Notice the size of the data here .

The direct idea of this problem is to directly use a cycle to accumulate , However , When the data scale is large , such “ violence ” This method often results in timeouts . At this point you need to think about other ways . You can try , If you use 1000000000 As input to your program , Can your program run within the time limit specified above .

Another point worth noting is that the size of the answer is not in the default integer of your language (int) Within the scope of , If you use integers to save results , It can lead to wrong results .

If you use C++ or C Language and ready to use printf Output results , Then your format string should be written as %I64d To output long long Type integer .

Code ：

#include<iostream>
using namespace std;
int main()
{
    int i,n;
    long  long sum=0;
    cin>>n;
    sum=(1+n)*((n*1.0)/2);
    cout<<sum<<endl;
    return 0;
}

The title is simple. , But pay attention to the running time limit , So find your own rules ,1+2+3+...+n=(1+n)*(n*1.0/2);

Also, the variables that save the final results should be able to store big data .（long long type ）