这题穷举举到大概N=210就很慢了，不过这个题没有让我们给出相应的式子，参考了几个文章，学习到了这种方法：每一次把一个加号改为减号的时候 此式子的值比原式减小了一个偶数，因此，我们只需要判断 1+2+...+k=S  S-N是不是偶数就可以了 。

题目及AC代码如下：

The problem

Given the following formula, one can set operators ‘+‘ or ‘-‘ instead of each ‘?‘, in order to obtain a given k
? 1 ? 2 ? ... ? n = k

For example: to obtain k = 12 , the expression to be used will be:
- 1 + 2 + 3 + 4 + 5 + 6 - 7 = 12
with n = 7

The Input

The first line is the number of test cases, followed by a blank line.

Each test case of the input contains integer k (0<=|k|<=1000000000).

Each test case will be separated by a single line.

The Output

For each test case, your program should print the minimal possible n (1<=n) to obtain k with the above formula.

Print a blank line between the outputs for two consecutive test cases.

Sample Input

2

12

-3646397

Sample Output

7

2701

UVA 10025 The ? 1 ? 2 ? ... ? n = k problem,布布扣,bubuko.com

UVA 10025 The ? 1 ? 2 ? ... ? n = k problem

原文：http://www.cnblogs.com/VOID-133/p/3579029.html