A full binary tree is a binary tree where each node has exactly 0 or 2 children.
Return a list of all possible full binary trees with N nodes. Each element of the answer is the root node of one possible tree.
Each node of each tree in the answer must have node.val = 0.
You may return the final list of trees in any order.

You are given an array A of strings.
Two strings S and T are special-equivalent if after any number of moves, S == T.
A move consists of choosing two indices i and j with i % 2 == j % 2, and swapping S[i] with S[j].
Now, a group of special-equivalent strings from A is a non-empty subset S of A such that any string not in S is not special-equivalent with any string in S.
Return the number of groups of special-equivalent strings from A.

Example 1:
Input: [“a”,”b”,”c”,”a”,”c”,”c”]
Output: 3
Explanation: 3 groups [“a”,”a”], [“b”], [“c”,”c”,”c”]

Example 2:
Input: [“aa”,”bb”,”ab”,”ba”]
Output: 4
Explanation: 4 groups [“aa”], [“bb”], [“ab”], [“ba”]

On a N * N grid, we place some 1 * 1 * 1 cubes.
Each value v = grid[i][j] represents a tower of v cubes placed on top of grid cell (i, j).
Return the total surface area of the resulting shapes.

Example 1:
Input: [[2]]
Output: 10

Example 2:
Input: [[1,2],[3,4]]
Output: 34

嗨呀，之前在dilidili上看到好多有意思的东西，像什么windows主题换肤啊，QQ主题换肤啊，输入法主题换肤啊，感觉都好骚啊！这些画师太秀了，忍不住就先弄了个最简单的输入法换肤玩一玩。

555555，有个人就是不告诉我怎么导进来，气的我只好自己疯狂百度，发现这个方法原来是通用的，就是做图有点点麻烦。注意如果什么操作都不做，直接从贴吧把表情拷贝过来，你会发现表情很模糊，并且可能有白底，看起来超丑！所以一定要操作一下，最后效果如下：

Given an array of integers A, consider all non-empty subsequences of A.
For any sequence S, let the width of S be the difference between the maximum and minimum element of S.
Return the sum of the widths of all subsequences of A.
As the answer may be very large, return the answer modulo 10^9 + 7.

Example 1:
Input: [2,1,3]
Output: 6
Explanation:
Subsequences are [1], [2], [3], [2,1], [2,3], [1,3], [2,1,3].
The corresponding widths are 0, 0, 0, 1, 1, 2, 2.
The sum of these widths is 6.
这道题还算有点意思

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Solve a given equation and return the value of x in the form of string “x=#value”. The equation contains only ‘+’, ‘-‘ operation, the variable x and its coefficient.
If there is no solution for the equation, return “No solution”.
If there are infinite solutions for the equation, return “Infinite solutions”.
If there is exactly one solution for the equation, we ensure that the value of x is an integer.

Example 1:
Input: “x+5-3+x=6+x-2”
Output: “x=2”

An encoded string S is given. To find and write the decoded string to a tape, the encoded string is read one character at a time and the following steps are taken:
If the character read is a letter, that letter is written onto the tape.
If the character read is a digit (say d), the entire current tape is repeatedly written d-1 more times in total.
Now for some encoded string S, and an index K, find and return the K-th letter (1 indexed) in the decoded string.

Example 1:
Input: S = “leet2code3”, K = 10
Output: “o”
Explanation:
The decoded string is “leetleetcodeleetleetcodeleetleetcode”.
The 10th letter in the string is “o”.

The i-th person has weight people[i], and each boat can carry a maximum weight of limit.
Each boat carries at most 2 people at the same time, provided the sum of the weight of those people is at most limit.
Return the minimum number of boats to carry every given person. (It is guaranteed each person can be carried by a boat.)

Example 1:
Input: people = [1,2], limit = 3
Output: 1
Explanation: 1 boat (1, 2)

On a N * N grid, we place some 1 * 1 * 1 cubes that are axis-aligned with the x, y, and z axes.

Each value v = grid[i][j] represents a tower of v cubes placed on top of grid cell (i, j).

Now we view the projection of these cubes onto the xy, yz, and zx planes.

A projection is like a shadow, that maps our 3 dimensional figure to a 2 dimensional plane.

Here, we are viewing the “shadow” when looking at the cubes from the top, the front, and the side.

Return the total area of all three projections.