Sum Problem

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于 2019-06-30 21:28:50 发布

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Sum Problem

Time Limit: 1000/500 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 630351 Accepted Submission(s): 159522

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

100

Sample Output

5050

#include<iostream>
#include<map>
using namespace std;
typedef long long ll;
map<int,ll>m;
void sum(int a){
	ll res=0;
	res+=m[a-1];
	res+=a;
	m[a]=res;
}
int main(){
	int n=1e5;
	for(int i=1;i<=n;i++){
		sum(i);
	}
	int x;
	while(cin>>x){
		cout<<m[x]<<endl;
		cout<<endl;
	}
	return 0;
}