# [hdu 4609][13多校] 3-idiots

### Problem Description

King OMeGa catched three men who had been streaking in the street. Looking as idiots though, the three men insisted that it was a kind of performance art, and begged the king to free them. Out of hatred to the real idiots, the king wanted to check if they were lying. The three men were sent to the king's forest, and each of them was asked to pick a branch one after another. If the three branches they bring back can form a triangle, their math ability would save them. Otherwise, they would be sent into jail.
However, the three men were exactly idiots, and what they would do is only to pick the branches randomly. Certainly, they couldn't pick the same branch - but the one with the same length as another is available. Given the lengths of all branches in the forest, determine the probability that they would be saved.

# <从入门到崩溃>快速傅里叶变换学习笔记

### 储备知识

#### 多项式

##### 系数表达式

$f(x)=\sum_{i=0}^{n}a_{i}x^{i}$为一$n$次多项式，其中，$a_{i}$称作系数。