## 看到的一題

Given $a > 0, a\neq 1$, $\forall n \in \mathbb{N}$, we have

$$\frac{1+a^2+a^4+\cdots + a^{2n}}{a+a^3+\cdots+a^{2n-1}} > \frac{n+1}{n}$$

## LeetCode 0015－3Sum

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Notice that the solution set must not contain duplicate triplets.