### 破解微信禁止模拟器登录

[ + ]

 1 ↑ . 微信 5.2.1 for Android 全新发布. . [2015-01-18].

### 求两个集合/数组的交集

A = [9, 1, 4, 2, 5] k个整数
B = [3, 1, 8, 7, 6, 5] n个整数
Intersection => [1, 5]

# 推导

1-2-3-4
|___|

In[]:=Reduce[Mod[n – 1, 3] == Mod[2n – 1, 3], n, Integers]Out[]:=$$c_1\in \mathbb{Z}\land n=3 c_1$$

In[]:=

### Fraction to Recurring Decimal正则表达式、循环小数复习

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

• Given numera[……]

### Mathematica笔记：函数类型

Mathematica的函数，按是否对参数求值为分二类：1、必求值，2、可能求值。

# 题目

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exi[……]

# 题目

Given an unsorted array, find the maximum difference between the successive elements in its sorted form.

Try to solve it in linear time/space.

Return 0 if the array contains less than 2 elements.

You may assume all elements in the array[……]

# 协方差矩阵

$$\bar{X}$$为矩阵X每一列的平均数。

\bar{X}=\begin{bmatrix}
\mu_1 & \mu_2 & \cdots & \mu_p\\
\mu_1 & \mu_2 & \cdots & \mu_p\\
\vdots & \vdots & \ddots & \vdots \\
\mu_1[……]

# 特征值和（右）特征向量的定义

$$A\vec{x}=\lambda\vec{x}$$