Sum

描述：

Consider the natural numbers from 1 to N. By associating to each number a sign (+ or -) and calculating the value of this expression we obtain a sum S. The problem is to determine for a given sum S the minimum number N for which we can obtain S by associating signs for all numbers between 1 to N.

For a given S, find out the minimum value N in order to obtain S according to the conditions of the problem.

输入：

The only line contains in the first line a positive integer S (0< S <= 100000) which represents the sum to be obtained.

输出：

The output will contain the minimum number N for which the sum S can be obtained.

输入样例：

12

0

输出样例：

7

3

解题思路：先对1~N求和，求出最大的范围，然后每当减一个数就是要减掉两倍的，就是减去偶数，所以只要Sum-sum是偶数即可。

代码如下：

Code:

1. #include<iostream>
2. usingnamespacestd;
3. intmain()
4. {
5. intstate=0;
6. intn;
7. cin>>n;
8. for(inti=1;;i++)
9. {
10. ints=i*(i+1)/2;
11. if(s<n)
12. continue;
13. if((s-n)%2==0)
14. {
15. cout<<i<<endl;
16. break;
17. }
18. }
19. return0;
20. }